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298 Commits

Author SHA1 Message Date
nobody
8c6f266370 This commit was manufactured by cvs2svn to create tag
'version_0-8-1'.

[SVN r18620]
2003-05-30 21:52:34 +00:00
Bruno da Silva de Oliveira
bc112ba65f - Fixed bug in the generation of virtual methods.
[SVN r18619]
2003-05-30 21:52:33 +00:00
Dave Abrahams
62ba322658 updated ImageMagick info.
[SVN r18597]
2003-05-29 14:00:00 +00:00
Dave Abrahams
02135b550d OpenSceneGraph has a web page
[SVN r18596]
2003-05-29 13:14:48 +00:00
Ralf W. Grosse-Kunstleve
ee4b06bb50 static keyword removed (Aye, Aye Sir David Abrahams!)
[SVN r18570]
2003-05-27 21:07:40 +00:00
Ralf W. Grosse-Kunstleve
16c5435ca8 fix typo
[SVN r18554]
2003-05-26 22:03:46 +00:00
Bruno da Silva de Oliveira
2595049748 - Added the Techniques section
[SVN r18552]
2003-05-26 21:10:41 +00:00
Ralf W. Grosse-Kunstleve
5911691c0d workaround for silly MIPSpro compiler
[SVN r18550]
2003-05-26 19:46:05 +00:00
Ralf W. Grosse-Kunstleve
e369bddc84 avoid use of sizeof to enable compilation with buggy gcc 3.3; change as per David Abrahams' instructions
[SVN r18549]
2003-05-26 19:06:00 +00:00
Ralf W. Grosse-Kunstleve
dccf2bbb4a Tru64 cxx compatibility
[SVN r18548]
2003-05-26 19:03:24 +00:00
Bruno da Silva de Oliveira
eaab3fc038 - Fixed link to the tutorial
[SVN r18519]
2003-05-23 21:06:22 +00:00
Bruno da Silva de Oliveira
858e1aba67 - Support for global variables
- Bug fixes in ClassExporter


[SVN r18518]
2003-05-23 20:37:35 +00:00
Bruno da Silva de Oliveira
19eff7791d - HeaderExporter now doesn't export names that begin with "_"
- Bug in ClassExporter, was adding an attribute to the members of base classes in GenerateVirtualMethods


[SVN r18516]
2003-05-23 19:13:52 +00:00
Bruno da Silva de Oliveira
c81af4ffe0 - Two new questions, about compiling time and creating packages.
[SVN r18515]
2003-05-23 18:01:39 +00:00
Dave Abrahams
9675e4233b Fix a bug in dangling reference/pointer detection. Thanks to Daniel
Paull <dlp-at-fractaltechnologies.com> for reporting it.


[SVN r18498]
2003-05-22 15:13:22 +00:00
Dave Abrahams
e6a176bb1e Add initializer list for silly GCC
[SVN r18491]
2003-05-22 01:35:53 +00:00
Dave Abrahams
ff0980914b reinstate workarounds for vc7
[SVN r18490]
2003-05-22 01:34:04 +00:00
Dave Abrahams
43e5ccd0a7 object_core.hpp - allow wrapping of objects which take object managers in their constructors.
forward.hpp
pointer_holder.hpp
value_holder.hpp
test/long.[py/cpp]

pointee.hpp,    - begin making borland work.
cv_category.hpp,
referent_storage.hpp
instance.hpp

self.hpp        - removed flotsam

signature.hpp   - use vector instead of list

destroy.hpp     - removed needless complication

make_keyword_range_fn.hpp - support for simpler init using vectors

class_converters.hpp - workaround for pro7

inheritance.hpp - simplified; took out pro7 workarounds; factored out
                  inheritance_query.hpp to reduce recompilation
                  dependencies

make_ptr_instance.hpp - add missing typename

registry.cpp    - add a little invariant checking for metrowerks

class.cpp       - stopped relying on class_id typedef

test/data_members.cpp - added a few more tests to make sure things compile at least.
test/destroy_test.cpp - removed cheating has_trivial_destructor tests
test/enum.cpp         - added some pro7 workarounds
test/virtual_functions.[py/cpp] - added _some_ tests for callbacks which return by reference.


[SVN r18489]
2003-05-21 22:17:23 +00:00
Dave Abrahams
66d6272942 Use mpl::vector and simplify constructor generation so we don't have
to constantly reverse lists.


[SVN r18487]
2003-05-21 21:53:30 +00:00
Dave Abrahams
2f1b828967 Getter setter bugfixes for attribute access
[SVN r18486]
2003-05-21 21:52:26 +00:00
Dave Abrahams
622636dcf1 Killed unneeded #include
[SVN r18485]
2003-05-21 21:51:03 +00:00
Dave Abrahams
0c22c276bf Workaround CW bug
[SVN r18472]
2003-05-20 19:01:44 +00:00
Bruno da Silva de Oliveira
7a4a79c74e no message
[SVN r18461]
2003-05-20 03:17:19 +00:00
Bruno da Silva de Oliveira
06f454e1d3 - Some small memory improvements
[SVN r18459]
2003-05-20 01:35:13 +00:00
Bruno da Silva de Oliveira
c1dbd52de1 - Fixed bug where functions with the same name where not being exported correctly
[SVN r18458]
2003-05-19 23:58:35 +00:00
Dave Abrahams
c3f5679188 Bug fix
[SVN r18372]
2003-05-08 20:18:14 +00:00
Bruno da Silva de Oliveira
97e2628f95 - Fixed bug where GCCXML was generating more than one declaration of a given class
[SVN r18359]
2003-05-08 10:38:51 +00:00
Dave Abrahams
6cecfcb704 restore from disk crash
[SVN r18353]
2003-05-08 02:19:10 +00:00
Ralf W. Grosse-Kunstleve
022a5a16f5 Python 2.3b1 compatibility: LONG_LONG -> PY_LONG_LONG
[SVN r18337]
2003-05-01 05:19:47 +00:00
Bruno da Silva de Oliveira
a39a834e75 - Now trying to export forward declared classes gives a warning.
- Forward-declared classes are ignored with AllFromHeader
- Bug: now it's possible to exclude classes, functions and enums from AllFromHeader


[SVN r18289]
2003-04-23 00:42:34 +00:00
Dave Abrahams
2a1210384a Warning suppression from Dominique Devriese <dominique.devriese-at-student.kuleuven.ac.be>
[SVN r18288]
2003-04-22 14:21:37 +00:00
Bruno da Silva de Oliveira
d497611069 - New code (more generic) for declaring the smart pointer converters
[SVN r18269]
2003-04-16 22:35:09 +00:00
Dave Abrahams
46d8786f5a Tweak citations, etc.
[SVN r18265]
2003-04-16 16:12:34 +00:00
Dave Abrahams
b8028729eb NULL shared_ptr conversions, more tests for custom to-python shared_ptr registrations
[SVN r18263]
2003-04-16 14:32:14 +00:00
Dave Abrahams
30e7768a87 warning suppression
[SVN r18261]
2003-04-16 14:29:27 +00:00
Dave Abrahams
10dc663e07 *** empty log message ***
[SVN r18259]
2003-04-16 13:39:28 +00:00
Joel de Guzman
42fc57d761 tweaks
[SVN r18255]
2003-04-15 12:48:27 +00:00
Dave Abrahams
74cd2f4844 Fix bug report from Jacek Generowicz <jacek.generowicz-at-cern.ch>
[SVN r18254]
2003-04-15 11:10:53 +00:00
Bruno da Silva de Oliveira
a15135f1c1 - Fixed a inheritance bug, and added a test for it.
[SVN r18251]
2003-04-14 23:34:33 +00:00
Dave Abrahams
ccd84c0be6 Small changes to support new iterator adaptors in sandbox
[SVN r18212]
2003-04-09 11:57:59 +00:00
Joel de Guzman
510215f284 typo fixes
[SVN r18201]
2003-04-08 01:20:58 +00:00
Bruno da Silva de Oliveira
c7ea0aacd6 - Lots of fixes in the documentation
- Fixed support for return_opaque_pointer policy


[SVN r18199]
2003-04-08 01:01:32 +00:00
Bruno da Silva de Oliveira
f7f089d2d4 - Fixed bug where the order of instantiations in the --multiple mode could end up wrong
[SVN r18198]
2003-04-07 18:15:50 +00:00
Bruno da Silva de Oliveira
82721c77a1 - now includes documentation in the distribution
[SVN r18197]
2003-04-07 12:13:02 +00:00
Bruno da Silva de Oliveira
1c9bf7d91c - Generating code for the improved support of static data members of Boost.Python
[SVN r18193]
2003-04-06 20:47:10 +00:00
Bruno da Silva de Oliveira
9bf78396cb - fixed bug where return_opaque_pointer was not being added to the user context
[SVN r18192]
2003-04-06 13:43:19 +00:00
Bruno da Silva de Oliveira
d994e4719c - New unittests for linux, now testing single and multi modes
[SVN r18189]
2003-04-05 18:14:52 +00:00
Bruno da Silva de Oliveira
44b886bb76 - Added a new line after the end of the "_main.cpp" files in multiple mode
[SVN r18188]
2003-04-05 18:11:44 +00:00
Bruno da Silva de Oliveira
8d2f012bcf - added new option for generating bindings: --multiple
- some refactoring of the code
- now detects forward declarations and prints a warning about them


[SVN r18187]
2003-04-05 17:05:12 +00:00
Dave Abrahams
a86deed5f6 dummy
[SVN r18158]
2003-04-02 12:57:33 +00:00
Dave Abrahams
3fd9ad7a60 implement static data members
[SVN r18157]
2003-04-02 12:56:37 +00:00
Bruno da Silva de Oliveira
319a5cf97c - Added the experimental command line option -R, which is a workaround a gccxml's preprocessor bug
[SVN r18138]
2003-03-30 21:06:10 +00:00
Bruno da Silva de Oliveira
0fd503d6af - Bug where the full name of the operator wasn't used in the declaration
- Now converter operators that return char* or string are automatically named __str__ in Python
- Update documentation with info about Psyco


[SVN r18127]
2003-03-28 21:02:24 +00:00
Bruno da Silva de Oliveira
bf696026bd - Performance improvements (better psyco support, cache in CppParser)
[SVN r18123]
2003-03-28 12:47:15 +00:00
Bruno da Silva de Oliveira
734657244b - Changed the error message about missing policies.
[SVN r18118]
2003-03-27 23:40:59 +00:00
Bruno da Silva de Oliveira
d2470e4f9c - Fixed bug where virtual methods could end exported twice in the wrapper.
[SVN r18116]
2003-03-27 23:24:40 +00:00
Bruno da Silva de Oliveira
28a2792280 no message
[SVN r18107]
2003-03-27 17:23:52 +00:00
Bruno da Silva de Oliveira
cd985a33d8 - Added files to create a binary distribution
[SVN r18106]
2003-03-27 17:14:41 +00:00
Bruno da Silva de Oliveira
726d2beffd - Doc fix, about accessing the operators in the interface file
[SVN r18097]
2003-03-26 18:35:53 +00:00
Bruno da Silva de Oliveira
f04be3fc1b - No more "needs policy" warnings for functions that return PyObject*
[SVN r18096]
2003-03-26 15:25:38 +00:00
Bruno da Silva de Oliveira
b6927410d9 - Fixed stupid bug in HandlePolicy
[SVN r18095]
2003-03-26 15:06:14 +00:00
Bruno da Silva de Oliveira
44b2e1ef8b - Default policy for functions/methods that return const T& is now
return_value_policy<copy_const_reference>().


[SVN r18077]
2003-03-24 23:25:14 +00:00
Bruno da Silva de Oliveira
3d01e6af89 no message
[SVN r18067]
2003-03-23 18:29:11 +00:00
Bruno da Silva de Oliveira
00387b2076 - Documentation for smart-pointers
[SVN r18066]
2003-03-23 18:27:18 +00:00
Bruno da Silva de Oliveira
f9bf514801 - Added unittests for linux
[SVN r18065]
2003-03-23 18:23:09 +00:00
Bruno da Silva de Oliveira
fa27bddfab - added a case: wrapper for a virtual method
[SVN r18062]
2003-03-22 19:35:55 +00:00
Bruno da Silva de Oliveira
f27e8f8ddc no message
[SVN r18061]
2003-03-22 19:34:49 +00:00
Bruno da Silva de Oliveira
5b2623ff2e - bumped version number
[SVN r18060]
2003-03-22 19:33:33 +00:00
Bruno da Silva de Oliveira
a83a726b6e - Fixed bug where wrappers for virtual methods were ignored.
[SVN r18059]
2003-03-22 19:31:19 +00:00
Bruno da Silva de Oliveira
93df7e00a7 - Added new flags: -h, --help, -v, --version
[SVN r18058]
2003-03-22 18:20:16 +00:00
Bruno da Silva de Oliveira
6b7748a88d - Now exporting virtual methods from base classes too
[SVN r18057]
2003-03-22 18:19:25 +00:00
Bruno da Silva de Oliveira
f102c77fa2 no message
[SVN r18056]
2003-03-22 18:18:25 +00:00
Bruno da Silva de Oliveira
a4fa261b77 - New page about smart pointers, and misc fixes
[SVN r18055]
2003-03-22 18:16:01 +00:00
Dave Abrahams
8a15fefc6c update HippoDraw site
[SVN r18053]
2003-03-22 17:29:01 +00:00
Bruno da Silva de Oliveira
12a4cc16be - Added MANUAL support for shared_ptr and auto_ptrs. In the future, support should be automatic.
[SVN r18041]
2003-03-21 14:24:20 +00:00
Dave Abrahams
6335716342 fixed binary-ness
[SVN r18038]
2003-03-20 20:33:48 +00:00
Dave Abrahams
db0602ac2a *** empty log message ***
[SVN r18037]
2003-03-20 20:31:57 +00:00
Bruno da Silva de Oliveira
390ad530f1 - Bug: GenerateName in infos.py doesn't cover all possible cases.
[SVN r18028]
2003-03-20 04:55:38 +00:00
Dave Abrahams
6eb2e8d68a paper updates
[SVN r18027]
2003-03-20 02:56:22 +00:00
Dave Abrahams
b804b3b221 fix typo
[SVN r18025]
2003-03-20 02:53:47 +00:00
Joel de Guzman
936c1118bd Bump to v1.6.0
[SVN r18021]
2003-03-19 23:33:19 +00:00
Bruno da Silva de Oliveira
4ba7b8a8ff - Updated to reflect changes in declarations.py
[SVN r17997]
2003-03-19 05:55:28 +00:00
Bruno da Silva de Oliveira
70601e9da0 no message
[SVN r17995]
2003-03-19 05:54:26 +00:00
Bruno da Silva de Oliveira
c32d1f9614 - Fixed bug where the PointerDeclaration of functions and methods didn't have the & operator
[SVN r17994]
2003-03-19 05:03:49 +00:00
Dave Abrahams
e031f78ad4 news updates; added links to paper
[SVN r17993]
2003-03-19 03:57:59 +00:00
Bruno da Silva de Oliveira
7d0273051a - Fixed bug where an union that was a class member crashed pyste (unions are still not exported)
- Added support for int, double, float and long operators


[SVN r17989]
2003-03-19 02:49:18 +00:00
Bruno da Silva de Oliveira
29d537571b - Unit tests for the examples
[SVN r17987]
2003-03-19 02:47:29 +00:00
Dave Abrahams
39f243f76b Check in html and pdf versions
[SVN r17985]
2003-03-19 01:47:30 +00:00
Dave Abrahams
0712360cc9 Add funcptr FAQ
[SVN r17975]
2003-03-18 14:41:04 +00:00
Dave Abrahams
02c125cbb4 Add funcptr FAQ
[SVN r17974]
2003-03-18 14:40:09 +00:00
Bruno da Silva de Oliveira
13256fb7e9 - Fixed bugs in Linux
[SVN r17969]
2003-03-18 05:16:01 +00:00
Bruno da Silva de Oliveira
f11d757807 - Fixed bug where the permission bits were being copied to the tmp file
[SVN r17934]
2003-03-15 02:51:51 +00:00
Bruno da Silva de Oliveira
2e123849fb no message
[SVN r17931]
2003-03-14 23:39:04 +00:00
Bruno da Silva de Oliveira
2f6cfaf0e9 - Fixed definition of private default implementations
[SVN r17928]
2003-03-14 22:27:32 +00:00
Bruno da Silva de Oliveira
f9b216d6f9 - Now generating wrappers for protected and private virtual methods
[SVN r17924]
2003-03-14 21:12:55 +00:00
Dave Abrahams
5fdd10d77e respond to Ralf's suggestions
[SVN r17900]
2003-03-13 22:58:03 +00:00
Dave Abrahams
41de02d528 Added development history
[SVN r17899]
2003-03-13 22:05:50 +00:00
Ralf W. Grosse-Kunstleve
1c3d08f23a adjustment for MIPSpro
[SVN r17865]
2003-03-12 23:18:16 +00:00
Bruno da Silva de Oliveira
0f1dc1fd50 - fixed bug where non-public virtual methods where being exported
- fixed " call_method<%s>"  to " call_method< %s >"


[SVN r17860]
2003-03-12 21:26:45 +00:00
Dave Abrahams
cd06018820 opaque pointer conversions from Gottfried.Ganssauge@haufe.de
[SVN r17859]
2003-03-12 17:56:41 +00:00
Dave Abrahams
7816eb6344 fix copyrights
[SVN r17841]
2003-03-12 13:51:17 +00:00
Dave Abrahams
9813f4b55f Fix copyrights
[SVN r17840]
2003-03-12 13:50:18 +00:00
Dave Abrahams
f81ca21b22 opaque pointer conversions from Gottfried.Ganssauge@haufe.de
Acknowledgements for all


[SVN r17834]
2003-03-12 12:47:44 +00:00
Bruno da Silva de Oliveira
f1b7620c9e no message
[SVN r17828]
2003-03-12 03:42:37 +00:00
Bruno da Silva de Oliveira
7d5c453f59 no message
[SVN r17825]
2003-03-12 01:39:28 +00:00
Bruno da Silva de Oliveira
bc4feb42b5 - fixed "deepcopy" of infos bug
[SVN r17824]
2003-03-12 01:32:48 +00:00
Bruno da Silva de Oliveira
ca9920874f - fixed default arguments in virtual methods
[SVN r17823]
2003-03-12 01:32:00 +00:00
Bruno da Silva de Oliveira
415991f6fc - added a link to the Pyste documentation
[SVN r17806]
2003-03-11 03:34:28 +00:00
Bruno da Silva de Oliveira
20c52def19 - first version
[SVN r17805]
2003-03-11 03:29:22 +00:00
Bruno da Silva de Oliveira
7dcacbcfc4 - first version
[SVN r17804]
2003-03-11 03:20:24 +00:00
Ralf W. Grosse-Kunstleve
34bf1560a9 non-template function make_function1 must be inline
[SVN r17791]
2003-03-09 17:26:06 +00:00
Dave Abrahams
39195ac97a Fix for older EDGs
[SVN r17786]
2003-03-08 12:36:18 +00:00
Dave Abrahams
6aa71e1f72 Remove flotsam
[SVN r17783]
2003-03-08 08:53:19 +00:00
Dave Abrahams
257a6c45f8 Remove flotsam
[SVN r17782]
2003-03-08 08:51:45 +00:00
Dave Abrahams
d34a11b584 Fix for Python 2.3 long->int conversion behavior change
[SVN r17779]
2003-03-08 05:28:54 +00:00
Dave Abrahams
ca64c96133 Added dangling_reference FAQ
Various idiomatic MPL cleanups in indirect_traits.hpp
raw_function support
Patches for CWPro7.2
Patches to pass tests under Python 2.3 with the new bool type.
Tests for member operators returning const objects
Fixes for testing Boost.Python under Cygwin


[SVN r17777]
2003-03-08 03:53:19 +00:00
Ralf W. Grosse-Kunstleve
ff734e3269 MIPSpro compatibility
[SVN r17772]
2003-03-08 00:25:47 +00:00
Dave Abrahams
d028a60cc2 Workaround for vc7 bug (and regression test)
[SVN r17708]
2003-03-03 17:21:30 +00:00
Dave Abrahams
577f58149c tests for operators returning const objects
[SVN r17700]
2003-03-02 22:11:20 +00:00
Dave Abrahams
4b97e191b8 Fix formatting errors
[SVN r17697]
2003-03-02 15:25:35 +00:00
Ralf W. Grosse-Kunstleve
15a148ab10 minor polishing, corrections
[SVN r17696]
2003-03-02 02:50:49 +00:00
Dave Abrahams
5ac7741ca9 Updates for ACCU
[SVN r17695]
2003-03-02 00:55:07 +00:00
Dave Abrahams
4c7cff6e8e fix bad link
[SVN r17691]
2003-03-01 18:25:41 +00:00
Dave Abrahams
c6ca85b525 Added embedding tutorial from Dirk Gerrits. Thanks, Dirk!
[SVN r17690]
2003-03-01 18:19:38 +00:00
Dave Abrahams
99f45b474e Fix broken links
[SVN r17671]
2003-02-27 13:07:41 +00:00
Dave Abrahams
ee44c90e85 Fixes for Python and Cygwin testing
[SVN r17667]
2003-02-27 02:20:01 +00:00
Dave Abrahams
2c4fa48f46 Fixes for Intel5
[SVN r17658]
2003-02-26 13:48:16 +00:00
Aleksey Gurtovoy
90fcd9369d MPL names/directory structure refactoring
[SVN r17651]
2003-02-25 23:11:41 +00:00
Dave Abrahams
923feda9f7 update
[SVN r17627]
2003-02-25 03:54:38 +00:00
Dave Abrahams
6d7d2ea5fe initial checkin
[SVN r17626]
2003-02-25 03:31:36 +00:00
Dave Abrahams
4874a1801b Improved Boost.Python build reliability and documentation.
[SVN r17623]
2003-02-25 02:15:55 +00:00
Dave Abrahams
479d8fc0f6 shared_ptr deleter introspection support
miscellaneous cleanups and MPL idiom-izing


[SVN r17622]
2003-02-25 01:03:40 +00:00
Dave Abrahams
1c346b2531 fix metafunctions for MPL
[SVN r17621]
2003-02-25 00:57:33 +00:00
Dave Abrahams
5cdebaf896 gcc-2.95 workaround
[SVN r17620]
2003-02-25 00:56:55 +00:00
Joel de Guzman
600602f9dc Tutorial updates
[SVN r17598]
2003-02-23 03:53:36 +00:00
Joel de Guzman
2a530bb9d2 Tutorial updates. Added virtual functions with default implementations and reshufled the overloading topics to discuss manual overloading first.
[SVN r17597]
2003-02-23 02:23:15 +00:00
Dave Abrahams
acdad5caf3 better auto_ptr support
[SVN r17592]
2003-02-22 18:11:08 +00:00
Dave Abrahams
b42b243287 vc++7.1 bug workarounds
[SVN r17591]
2003-02-22 18:07:05 +00:00
Dave Abrahams
a76f5f3db7 mpl-ish cleanup
[SVN r17585]
2003-02-22 01:02:31 +00:00
Dave Abrahams
4e9f745d4a Fixups for cygwin
[SVN r17570]
2003-02-21 08:10:55 +00:00
Aleksey Gurtovoy
101961a7c6 remove old MSVC 6.5 workaround
[SVN r17564]
2003-02-20 21:31:46 +00:00
Aleksey Gurtovoy
29d1f860c1 ETI fixes
[SVN r17563]
2003-02-20 21:29:39 +00:00
Dave Abrahams
2663e73f1c Automatically add library-path values to RUN_PATH/RUN_LD_LIBRARY_PATH
[SVN r17562]
2003-02-20 20:28:05 +00:00
Aleksey Gurtovoy
1f9d0bb196 MSVC 7.0 ETI workaround
[SVN r17556]
2003-02-20 13:35:16 +00:00
Joel de Guzman
ff9f262fac tutorial update
[SVN r17512]
2003-02-18 18:44:16 +00:00
Dave Abrahams
472dc3bd41 made binary
[SVN r17320]
2003-02-11 17:30:23 +00:00
Dave Abrahams
6f91b93519 removed to make binary
[SVN r17319]
2003-02-11 17:29:27 +00:00
Joel de Guzman
47291f68b2 removed unnecessary file
[SVN r17318]
2003-02-11 12:18:47 +00:00
Ralf W. Grosse-Kunstleve
2b5ef3c572 Python 2.3 compatibility
[SVN r17271]
2003-02-07 18:56:16 +00:00
Ralf W. Grosse-Kunstleve
9c50496d93 second half of introduction rewritten; SWIG, SIP, CXX acknowledged as suggested by the PyConDC reviewers; technical points moved to Library Overview section
[SVN r17259]
2003-02-07 01:07:39 +00:00
Ralf W. Grosse-Kunstleve
80488e2f23 improved serialization and object interface sections; some sentences added to the end of the conclusion
[SVN r17258]
2003-02-06 22:42:36 +00:00
Dave Abrahams
ad8da7166b edits
[SVN r17257]
2003-02-06 20:56:26 +00:00
Dave Abrahams
55cb918c51 Add ownership question
[SVN r17250]
2003-02-06 13:50:53 +00:00
Dave Abrahams
ac55c5ccf7 Add FAQ reference
[SVN r17249]
2003-02-06 13:50:31 +00:00
Ralf W. Grosse-Kunstleve
5bcf90766f draft thinking hybrid section added
[SVN r17242]
2003-02-05 19:58:43 +00:00
Dave Abrahams
8f12fdea4a Remove workaround patches
[SVN r17128]
2003-01-31 18:37:11 +00:00
Dave Abrahams
6f687ee402 Added a FAQ
[SVN r17010]
2003-01-23 17:38:57 +00:00
Dave Abrahams
9dfe98abb0 bug fix + regression test
[SVN r17002]
2003-01-23 04:32:10 +00:00
Dave Abrahams
399cf70b92 Add staticmethod support from Nikolay Mladenov <nickm-at-sitius.com>
[SVN r16946]
2003-01-19 19:12:30 +00:00
Joel de Guzman
571790097a minor error fixed PodBayDoorException const& x
[SVN r16926]
2003-01-18 01:44:48 +00:00
Ralf W. Grosse-Kunstleve
21f3c7c8c2 Mac OS X status
[SVN r16904]
2003-01-15 06:19:23 +00:00
Vladimir Prus
9d26167ec1 Change use-requirements to usage-requirements in some library Jamfiles.
[SVN r16884]
2003-01-13 12:31:12 +00:00
Vladimir Prus
ba4906d05c Update V2 Jamfile for Boost.
[SVN r16882]
2003-01-13 10:05:01 +00:00
Dave Abrahams
e13a11eb7f Fix dict bug
[SVN r16866]
2003-01-11 00:18:59 +00:00
Ralf W. Grosse-Kunstleve
72b214b8db details from the introduction moved to design goals section
[SVN r16864]
2003-01-10 19:22:13 +00:00
Ralf W. Grosse-Kunstleve
84a8fb71b8 meager result after a real hard try
[SVN r16863]
2003-01-10 19:00:05 +00:00
Dave Abrahams
4f5272cab9 Folded in Ralf's first set of edits
[SVN r16856]
2003-01-10 15:17:46 +00:00
Dave Abrahams
5895047e23 Initial Checkin
[SVN r16855]
2003-01-10 15:11:05 +00:00
Dave Abrahams
50bcf8db34 Apply workarounds for msvc-stlport
[SVN r16854]
2003-01-10 15:04:05 +00:00
Dave Abrahams
7defd3bbed support for BOOST_PYTHON_STATIC_MODULE
clarification


[SVN r16788]
2003-01-07 18:03:17 +00:00
Dave Abrahams
b9ecc931b0 support for BOOST_PYTHON_STATIC_MODULE
[SVN r16787]
2003-01-07 17:44:06 +00:00
Dave Abrahams
b84a8fd737 support for BOOST_PYTHON_STATIC_MODULE
[SVN r16786]
2003-01-07 17:38:08 +00:00
Dave Abrahams
2b1a2ce09c Build static versions of the library too.
[SVN r16785]
2003-01-07 17:30:51 +00:00
Dave Abrahams
bcf36610e1 Check in VisualStudio support from Brett Calcott
[SVN r16717]
2002-12-29 17:27:52 +00:00
Dave Abrahams
1bb3254d4d Check in changes from Brett Calcott
[SVN r16716]
2002-12-29 16:53:48 +00:00
Beman Dawes
0f95d507c4 add or update See www.boost.org comments
[SVN r16708]
2002-12-27 16:51:53 +00:00
Dave Abrahams
aa58e21bda Bug fix, thanks to "Daniel Paull" <dlp@fractaltechnologies.com> for
reporting it.


[SVN r16698]
2002-12-24 04:49:33 +00:00
Dave Abrahams
eac0412d18 Fixed comment
[SVN r16676]
2002-12-21 22:12:31 +00:00
Dave Abrahams
0c8aa84f2f Enable automatic downcasting to registered classes for pointers, references, and smart pointers
[SVN r16673]
2002-12-20 18:19:18 +00:00
Dave Abrahams
3d874d1618 Major simplification of from_python conversion avoids registering
converters for every class.


[SVN r16669]
2002-12-20 00:04:40 +00:00
Dave Abrahams
b8edd99dbd Fix typo thanks to "William Trenker" <wtrenker@hotmail.com>
[SVN r16657]
2002-12-18 21:12:02 +00:00
Dave Abrahams
0df5ebf0fa Fix to allow accessing enums as data members
[SVN r16656]
2002-12-18 21:11:16 +00:00
Dave Abrahams
809535b934 clarifications
[SVN r16655]
2002-12-18 21:09:15 +00:00
Dave Abrahams
854e957b78 Workaround for MacOS GCC problem:
#define B0 0


[SVN r16654]
2002-12-18 19:09:34 +00:00
Dave Abrahams
df24f29232 nonconformance workaround from Gottfried.Ganssauge@HAUFE.DE
[SVN r16653]
2002-12-18 17:56:42 +00:00
Joel de Guzman
14c7d9ab14 typo error __rsub__ to __sub__
[SVN r16641]
2002-12-18 01:23:21 +00:00
Dave Abrahams
0e36ac6b72 Bug fix with construction of std::exception
[SVN r16625]
2002-12-16 21:14:30 +00:00
Dave Abrahams
0d2cdbbdfe GCC-2.95.2 workarounds
[SVN r16620]
2002-12-16 04:01:50 +00:00
Dave Abrahams
48f9bee21e Fix typo due to "William Trenker" <wtrenker@hotmail.com>
[SVN r16619]
2002-12-16 03:30:34 +00:00
Dave Abrahams
dd8fc049ff update news
[SVN r16607]
2002-12-14 00:17:22 +00:00
Dave Abrahams
abd22f1273 Handle unsigned long values that don't fit in a long.
[SVN r16606]
2002-12-14 00:10:52 +00:00
Dave Abrahams
4a5817d8ba enum export
[SVN r16604]
2002-12-13 20:04:34 +00:00
Dave Abrahams
eab084c9a2 enum export
[SVN r16603]
2002-12-13 19:58:24 +00:00
Dave Abrahams
80ea2383a7 Fix references to test library
[SVN r16585]
2002-12-10 23:05:38 +00:00
Dave Abrahams
ec76fbe027 Apply fixes from Dirk Gerrits <dirk@gerrits.homeip.net>
[SVN r16517]
2002-12-04 17:10:55 +00:00
Dave Abrahams
c772038e77 Apply fixes from Dirk Gerrits <dirk@gerrits.homeip.net>
[SVN r16506]
2002-12-04 13:36:03 +00:00
Dave Abrahams
59b1a8e71c Apply fixes from Dirk Gerrits <dirk@gerrits.homeip.net>
[SVN r16491]
2002-12-03 18:08:12 +00:00
Dave Abrahams
83c38876fe Simplify, simplify!!
[SVN r16483]
2002-12-02 22:57:47 +00:00
Dave Abrahams
9163c40a1a Further suppressed internal structure overflow problems which were cropping up with msvc6/7.
[SVN r16482]
2002-12-02 19:41:45 +00:00
Dave Abrahams
8b79380977 Less-taxing version of MPL lambda support for msvc6/7
[SVN r16480]
2002-12-02 16:18:35 +00:00
Dave Abrahams
34c9d895c8 Relaxed rules for using scope()
[SVN r16476]
2002-12-02 14:29:11 +00:00
Dave Abrahams
bf8bb83ec5 initial commit
[SVN r16473]
2002-12-02 12:40:18 +00:00
Dave Abrahams
328697952f automatic shared_ptr from_python conversions
[SVN r16467]
2002-12-02 01:37:39 +00:00
Dave Abrahams
3c19b89d9a Added reset()
[SVN r16466]
2002-12-01 16:14:44 +00:00
Dave Abrahams
ae9f394906 Added reset()
[SVN r16465]
2002-12-01 16:07:54 +00:00
Dave Abrahams
8467f36b80 Kill errant `typename'
[SVN r16464]
2002-12-01 04:40:05 +00:00
Dave Abrahams
43a9571b2c Fixed some technical problems with smart pointer support uncovered by
STLPort's debug mode. Unfortunately, had to expand Dereferenceable
requirements.


[SVN r16459]
2002-11-29 22:43:27 +00:00
Dave Abrahams
bbef71dc7d Progress on embedding example for unix.
[SVN r16458]
2002-11-29 20:23:54 +00:00
Dave Abrahams
c4df3c6562 Bug fix
[SVN r16442]
2002-11-27 14:23:07 +00:00
Dave Abrahams
0ad3bfd0ab Finally fixed polymorphism issues
[SVN r16435]
2002-11-27 07:04:32 +00:00
Dave Abrahams
fb7c450b76 Added is_reference_to_member_function_pointer
[SVN r16434]
2002-11-27 06:19:45 +00:00
Dave Abrahams
3fc70519cf Use boost is_polymorphic trait
[SVN r16433]
2002-11-27 06:19:13 +00:00
Dave Abrahams
98c2bf8ff2 Restored some missing v1 acknowledgements
[SVN r16432]
2002-11-27 02:18:52 +00:00
Dave Abrahams
f9c8bf15bb Restore CWPro7.2 to health. Also improve source organization slightly
[SVN r16416]
2002-11-26 02:47:17 +00:00
Dave Abrahams
a7e19ffb0b Refactored def() logic; moved assert_default_constructible into the
holder selectorbecause it was getting the wrong answer in some cases.


[SVN r16415]
2002-11-26 01:06:41 +00:00
Dave Abrahams
7609a1c7c6 Refactored; added static assertions against the specification of a default implementation
[SVN r16414]
2002-11-25 22:03:42 +00:00
Dave Abrahams
087e2d6e35 Add additional argument for default implementation of virtual functions
Fully commented


[SVN r16413]
2002-11-25 21:57:23 +00:00
Dave Abrahams
bb7710a5a2 Suppress GCC warning
[SVN r16412]
2002-11-25 21:19:35 +00:00
Dave Abrahams
0d582e0e79 Suppress GCC warning
[SVN r16411]
2002-11-25 20:54:37 +00:00
Dave Abrahams
3d0579cc08 Fix for VC7. For some reason lexical_cast doesn't seem to work out too
well. We'll need to be careful how we do type_info decoding once we
get the G++ fixes in.


[SVN r16410]
2002-11-25 20:52:49 +00:00
Dave Abrahams
352e390c7b Added tests for embedding demonstration
[SVN r16409]
2002-11-25 18:32:14 +00:00
Dave Abrahams
394037a127 updated
[SVN r16408]
2002-11-25 16:12:27 +00:00
Dave Abrahams
9d4e235cf6 add imul notes
[SVN r16397]
2002-11-25 03:41:34 +00:00
Dave Abrahams
cfbc1a6b48 Fully removed convertible() test from to_python converter protocol
Added tests for detecting unregistered classes when converting
indirectly to python.


[SVN r16396]
2002-11-25 01:57:57 +00:00
Dave Abrahams
31b8b58de9 CW workaround
[SVN r16393]
2002-11-24 21:45:09 +00:00
Dave Abrahams
a77a835694 New function invocation mechanism. This is the major groundwork for handling virtual functions with default implementations properly
[SVN r16390]
2002-11-24 03:26:28 +00:00
Dave Abrahams
dca5c5108b update
[SVN r16389]
2002-11-24 03:25:13 +00:00
Dave Abrahams
e14e4e156c New function invocation mechanism. This is the major groundwork for handling virtual functions with default implementations properly
[SVN r16388]
2002-11-24 02:43:24 +00:00
Dave Abrahams
05ce65d9d2 cleanup
[SVN r16387]
2002-11-23 22:31:13 +00:00
Dave Abrahams
b952e45036 Clip unneeded bind.hpp #include
[SVN r16386]
2002-11-23 22:30:48 +00:00
Dave Abrahams
4c630512fe Add missing add_const #include
[SVN r16385]
2002-11-23 22:18:23 +00:00
Dave Abrahams
0461d25de6 Add some qualification
[SVN r16384]
2002-11-23 22:16:55 +00:00
Dave Abrahams
2df120af72 Suppress a VC6 ICE
[SVN r16383]
2002-11-23 22:16:00 +00:00
Dave Abrahams
791b7e1a1b Tidy
[SVN r16381]
2002-11-23 20:03:49 +00:00
Dave Abrahams
f6f4e59473 Add notes about targeting Cygwin GCC
[SVN r16380]
2002-11-23 20:03:24 +00:00
Dave Abrahams
60924e82e2 On our way to polymorphism
[SVN r16374]
2002-11-23 02:59:45 +00:00
Dave Abrahams
75bd427b8e Bugfix
[SVN r16354]
2002-11-21 00:21:23 +00:00
Dave Abrahams
715118ce39 Bugfix
[SVN r16353]
2002-11-21 00:19:27 +00:00
Dave Abrahams
e3deb8275d update
[SVN r16351]
2002-11-20 23:07:32 +00:00
Dave Abrahams
c30e12f956 Make scope constructor explicit
[SVN r16350]
2002-11-20 22:58:57 +00:00
Ralf W. Grosse-Kunstleve
983b23db92 some missing html markup added
[SVN r16349]
2002-11-20 18:09:17 +00:00
Ralf W. Grosse-Kunstleve
ed2da9bedb list cctbx
[SVN r16348]
2002-11-20 18:01:44 +00:00
Dave Abrahams
409ff3c179 Added missing test
[SVN r16337]
2002-11-20 03:04:51 +00:00
Dave Abrahams
39eab72293 bugfixes
add_property now uses member_function_cast


[SVN r16335]
2002-11-20 01:14:16 +00:00
Dave Abrahams
71ea2bec86 more notes
[SVN r16330]
2002-11-19 17:39:40 +00:00
Dave Abrahams
c9af6ca94b Add missing copyright notices
[SVN r16329]
2002-11-19 17:39:17 +00:00
Dave Abrahams
72d5bac69f Add PSF copyright and change summary
[SVN r16327]
2002-11-19 16:56:55 +00:00
Dave Abrahams
6e0733afa2 Remove Tom's email address
[SVN r16315]
2002-11-19 01:33:07 +00:00
Dave Abrahams
e660cc50c6 Added Support link
[SVN r16299]
2002-11-17 05:59:12 +00:00
Dave Abrahams
e6b40f54cd initial commit
[SVN r16298]
2002-11-17 05:58:45 +00:00
Dave Abrahams
c2af21169d More notes
[SVN r16297]
2002-11-16 23:48:09 +00:00
Dave Abrahams
4f7af97f8c Bug fix thanks to Mark Russell <mrussell8081@pacbell.net>
[SVN r16296]
2002-11-16 23:23:45 +00:00
Dave Abrahams
57f54952c3 Bug fix thanks to Mark Russell <mrussell8081@pacbell.net>
[SVN r16295]
2002-11-16 23:22:30 +00:00
Dave Abrahams
b321b6d9db Tweaks, pseudocode
[SVN r16294]
2002-11-16 22:45:46 +00:00
Dave Abrahams
56c5227cf7 added note
[SVN r16293]
2002-11-16 22:28:28 +00:00
Dave Abrahams
ae2931ba1b initial commit
[SVN r16292]
2002-11-16 22:12:46 +00:00
Dave Abrahams
9e3589ec4d Added projects page link
[SVN r16290]
2002-11-16 20:50:21 +00:00
Dave Abrahams
61b7094dbd Added EMSolve entry
[SVN r16289]
2002-11-16 20:48:43 +00:00
Dave Abrahams
50ecc751d1 Added Fortress entry
[SVN r16288]
2002-11-16 20:39:56 +00:00
Dave Abrahams
bb536a0eaa One more step towards handling polymorphism: now we can sort out a 4th parameter
[SVN r16287]
2002-11-16 20:03:59 +00:00
Dave Abrahams
8b7527318d vc6/7 workaround
[SVN r16286]
2002-11-16 20:01:44 +00:00
Dave Abrahams
f2ac0145da is_reference_to_function_pointer implementation
[SVN r16278]
2002-11-16 06:55:04 +00:00
Dave Abrahams
06fe0f1bcc is_reference_to_function implementation
[SVN r16276]
2002-11-16 06:00:52 +00:00
Dave Abrahams
7ea2447246 Bug fix
[SVN r16273]
2002-11-16 03:38:24 +00:00
Dave Abrahams
0adf4477a3 vc7.1 workaround
[SVN r16267]
2002-11-16 00:45:26 +00:00
Dave Abrahams
b3311fd59d *** empty log message ***
[SVN r16266]
2002-11-15 22:19:40 +00:00
Dave Abrahams
ae109f13a2 *** empty log message ***
[SVN r16260]
2002-11-15 17:29:15 +00:00
Dave Abrahams
cb1901e111 initial commit
[SVN r16259]
2002-11-15 17:02:31 +00:00
Dave Abrahams
bbc052bedc Fix example
[SVN r16256]
2002-11-15 12:25:29 +00:00
Dave Abrahams
f2797ec262 Auto-detection of class memebers wrapped with make_getter()
[SVN r16241]
2002-11-14 17:41:13 +00:00
Dave Abrahams
a21727741f c1204 workaround documented
[SVN r16235]
2002-11-14 12:16:40 +00:00
Dave Abrahams
5f022269b1 Added News page, links back to top of docs
[SVN r16229]
2002-11-14 02:09:43 +00:00
Dave Abrahams
0e76fcf706 auto_ptr support
[SVN r16228]
2002-11-14 01:40:16 +00:00
Dave Abrahams
6b4dc2901d Fix broken link
[SVN r16227]
2002-11-13 22:56:41 +00:00
Dave Abrahams
bcf864fce3 Attempt to handle derived target types
[SVN r16224]
2002-11-13 17:22:48 +00:00
Dave Abrahams
0168d8fbc8 Be more explicit about the Cygwin stuff
[SVN r16215]
2002-11-12 19:36:19 +00:00
Dave Abrahams
88b1c1b926 Allow member pointers from base classes in def_readonly and
def_readwrite.


[SVN r16214]
2002-11-12 17:48:56 +00:00
Dave Abrahams
1f93827b63 Squash bogus warnings
[SVN r16196]
2002-11-11 13:49:09 +00:00
Dave Abrahams
8e3ba0bba3 Improve error messages
[SVN r16147]
2002-11-07 14:41:40 +00:00
Dave Abrahams
42a0441cb8 Doc fix from "Brett Calcott" <brett.calcott@paradise.net.nz>
[SVN r16145]
2002-11-07 13:12:05 +00:00
Joel de Guzman
7b091b86d2 tutorial tweaks
[SVN r16004]
2002-10-28 08:30:31 +00:00
Dave Abrahams
f346eaf693 grammar fix
[SVN r16001]
2002-10-28 07:33:01 +00:00
Dave Abrahams
038be89766 Build with Cygwin
[SVN r16000]
2002-10-28 04:22:14 +00:00
Dave Abrahams
a682dd9362 Fix a doc bug
[SVN r15981]
2002-10-25 04:47:39 +00:00
Joel de Guzman
387e8aadc6 changes to no_init and deriving classes
[SVN r15979]
2002-10-24 21:33:40 +00:00
Joel de Guzman
da273519fd added non_copyable to second version of class_<Base, BaseWrap...
[SVN r15978]
2002-10-24 21:12:37 +00:00
Joel de Guzman
8c2d6bb31b correction Var-->Num
[SVN r15977]
2002-10-24 20:50:04 +00:00
Vladimir Prus
3cb4a029e0 Improve Boost.Python building.
* libs/python/build/Jamfile.v2: Sense the location of python headers. Export
  include paths.

* libs/python/example/Jamfile.v2: New file.

* new/targets.jam: Use refined properties for constructed
    dependency properties

* new/gcc.jam: Handle 'find-library'. Set soname for dynamic libraries.

* new/builtin.jam: New feature 'find-library'.


[SVN r15966]
2002-10-23 12:12:00 +00:00
Dave Abrahams
037f952136 Added funding credit
[SVN r15948]
2002-10-16 22:47:44 +00:00
Dave Abrahams
7fc441801d Allow embedded nulls in std::string <-> Python string conversions,
patch from greg Landrum <greglandrum@mindspring.com>.

Tests by Dave A.


[SVN r15945]
2002-10-16 20:24:38 +00:00
Dave Abrahams
c389e057b4 Added return_by_value, enhanced data member support to handle constant members
[SVN r15935]
2002-10-15 15:46:34 +00:00
Dave Abrahams
2c7829f50e initial checkin
[SVN r15930]
2002-10-15 11:59:39 +00:00
Dave Abrahams
0593074196 Patches to support Synopsis
[SVN r15906]
2002-10-12 15:37:34 +00:00
Dave Abrahams
c7626150fc Move final RC_1_29_0 changes back to trunk
[SVN r15877]
2002-10-10 18:11:14 +00:00
Dave Abrahams
f6990fedc7 Move final RC_1_29_0 changes back to trunk
[SVN r15875]
2002-10-10 18:09:46 +00:00
Dave Abrahams
adb02376eb Move final RC_1_29_0 changes back to trunk
[SVN r15872]
2002-10-10 18:05:51 +00:00
Dave Abrahams
65b6eb0c27 Move final RC_1_29_0 changes back to trunk
[SVN r15871]
2002-10-10 18:01:58 +00:00
Dave Abrahams
654354e681 GCC 2.96 bug workaround
[SVN r15864]
2002-10-10 15:59:12 +00:00
488 changed files with 5367 additions and 46334 deletions

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@@ -1,66 +0,0 @@
# (C) Copyright David Abrahams 2001. Permission to copy, use, modify, sell and
# distribute this software is granted provided this copyright notice appears
# in all copies. This software is provided "as is" without express or implied
# warranty, and with no claim as to its suitability for any purpose.
#
# Boost.Python library Jamfile
# declare the location of this subproject relative to the root
subproject libs/python/build ;
# bring in the rules for python
SEARCH on <module@>python.jam = $(BOOST_BUILD_PATH) ;
include <module@>python.jam ;
if [ check-python-config ]
{
local bpl-linkflags ;
if $(UNIX) && ( $(OS) = AIX )
{
bpl-linkflags = <linkflags>"-e initlibboost_python" ;
}
dll boost_python
:
../src/numeric.cpp
../src/list.cpp
../src/long.cpp
../src/dict.cpp
../src/tuple.cpp
../src/str.cpp
../src/aix_init_module.cpp
../src/converter/from_python.cpp
../src/converter/registry.cpp
../src/converter/type_id.cpp
../src/object/enum.cpp
../src/object/class.cpp
../src/object/function.cpp
../src/object/inheritance.cpp
../src/object/life_support.cpp
../src/object/pickle_support.cpp
../src/errors.cpp
../src/module.cpp
../src/converter/builtin_converters.cpp
../src/converter/arg_to_python_base.cpp
../src/object/iterator.cpp
../src/object_protocol.cpp
../src/object_operators.cpp
:
$(BOOST_PYTHON_V2_PROPERTIES)
<define>BOOST_PYTHON_SOURCE
$(bpl-linkflags)
;
stage bin-stage : <dll>boost_python
:
<tag><debug>"_debug"
<tag><debug-python>"_pydebug"
:
debug release
;
}

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@@ -1,59 +0,0 @@
H1
{
FONT-SIZE: 200%
COLOR: #00007f
}
H2
{
FONT-SIZE: 150%;
}
H3
{
FONT-SIZE: 125%;
}
H4
{
FONT-SIZE: 108%;
}
BODY
{
FONT-SIZE: 100%;
BACKGROUND-COLOR: #ffffff
}
PRE
{
MARGIN-LEFT: 2pc;
FONT-SIZE: 80%;
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<h1 align="center">Boost.Python</h1>
<h2 align="center">Building and Testing</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="Reference">
<dt><a href="#requirements">Requirements</a></dt>
<dt><a href="#building">Building Boost.Python</a></dt>
<dd>
<dl class="index">
<dt><a href="#configuration">Configuration</a></dt>
<dt><a href="#results">Results</a></dt>
<dt><a href="#testing">Testing</a></dt>
</dl>
</dd>
<dt><a href="#building_ext">Building your Extension Module</a></dt>
<dt><a href="#variants">Build Variants</a></dt>
</dl>
<hr>
<h2><a name="requirements">Requirements</a></h2>
Boost.Python requires <a href="http://www.python.org">Python</a> 2.2 or
later.
<h2><a name="building">Building Boost.Python</a></h2>
<p>Every Boost.Python extension module must be linked with the
<code>boost_python</code> shared library. To build
<code>boost_python</code>, use <a href=
"../../../tools/build/index.html">Boost.Build</a> in the usual way from
the <code>libs/python/build</code> subdirectory of your boost
installation (if you have already built boost from the top level this may
have no effect, since the work is already done).</p>
<h3><a name="configuration">Configuration</a></h3>
You may need to configure the following variables to point Boost.Build at
your Python installation:
<table border="1" summary="build configuration variables">
<tr>
<th>Variable Name</th>
<th>Semantics</th>
<th>Default</th>
<th>Notes</th>
</tr>
<tr>
<td><code>PYTHON_ROOT</code></td>
<td>The root directory of your Python installation</td>
<td>Windows:&nbsp;<code>c:/tools/python</code>
Unix:&nbsp;<code>/usr/local</code></td>
<td>On Unix, this is the <code>--with-prefix=</code> directory used
to configure Python</td>
</tr>
<tr>
<td><code>PYTHON_VERSION</code></td>
<td>The The 2-part python Major.Minor version number</td>
<td><code>2.2</code></td>
<td>Be sure not to include a third number, e.g. <b>not</b>
"<code>2.2.1</code>", even if that's the version you have.</td>
</tr>
<tr>
<td><code>PYTHON_INCLUDES</code></td>
<td>path to Python <code>#include</code> directories</td>
<td>Autoconfigured from <code>PYTHON_ROOT</code></td>
</tr>
<tr>
<td><code>PYTHON_LIB_PATH</code></td>
<td>path to Python library object.</td>
<td>Autoconfigured from <code>PYTHON_ROOT</code></td>
</tr>
<tr>
<td><code>PYTHON_STDLIB_PATH</code></td>
<td>path to Python standard library modules</td>
<td>Autoconfigured from <code>PYTHON_ROOT</code></td>
</tr>
<tr>
<td><code>CYGWIN_ROOT</code></td>
<td>path to the user's Cygwin installation</td>
<td>
</td>
<td><a href="http://www.cygwin.com">Cygwin</a> only. This and the
following two settings are useful when building with multiple
toolsets on Windows, since Cygwin requires a different build of
Python.</td>
</tr>
<tr>
<td><code>GCC_PYTHON_ROOT</code></td>
<td>path to the user's Cygwin Python installation</td>
<td><code>$(CYGWIN_ROOT)/usr/local</code></td>
<td><a href="http://www.cygwin.com">Cygwin</a> only</td>
</tr>
<tr>
<td><code>GCC_DEBUG_PYTHON_ROOT</code></td>
<td>path to the user's Cygwin <code><a href=
"#variants">pydebug</a></code> build</td>
<td><code>$(CYGWIN_ROOT)/usr/local/pydebug</code></td>
<td><a href="http://www.cygwin.com">Cygwin</a> only</td>
</tr>
</table>
<h3><a name="results">Results</a></h3>
<p>The build process will create a
<code>libs/python/build/bin-stage</code> subdirectory of the boost root
(or of <code>$(ALL_LOCATE_TARGET)</code>, if you have set that variable),
containing the built libraries. The libraries are actually built to
unique directories for each toolset and variant elsewhere in the
filesystem, and copied to the <code>bin-stage</code> directory as a
convenience, so if you build with multiple toolsets at once, the product
of later toolsets will overwrite that of earlier toolsets in
<code>bin-stage</code>.</p>
<h3><a name="testing">Testing</a></h3>
<p>To build and test Boost.Python, start from the
<code>libs/python/test</code> directory and invoke</p>
<blockquote>
<pre>
bjam -sTOOLS=<i><a href=
"../../../tools/build/index.html#Tools">toolset</a></i> test
</pre>
</blockquote>
This will update all of the Boost.Python v1 test and example targets. The
tests are relatively quiet by default. To get more-verbose output, you
might try
<blockquote>
<pre>
bjam -sTOOLS=<i><a href=
"../../../tools/build/index.html#Tools">toolset</a></i> -sPYTHON_TEST_ARGS=-v test
</pre>
</blockquote>
which will print each test's Python code with the expected output as it
passes.
<h2><a name="building_ext">Building your Extension Module</a></h2>
Though there are other approaches, the easiest way to build an extension
module using Boost.Python is with Boost.Build. Until Boost.Build v2 is
released, cross-project build dependencies are not supported, so it works
most smoothly if you add a new subproject to your boost installation. The
<code>libs/python/example</code> subdirectory of your boost installation
contains a minimal example (along with many extra sources). To copy the
example subproject:
<ol>
<li>Create a new subdirectory in, <code>libs/python</code>, say
<code>libs/python/my_project</code>.</li>
<li>Copy <code><a href=
"../example/Jamfile">libs/python/example/Jamfile</a></code> to your new
directory.</li>
<li>Edit the Jamfile as appropriate for your project. You'll want to
change the "<code>subproject</code>" rule invocation at the top, and
the names of some of the source files and/or targets.</li>
</ol>
If you can't modify or copy your boost installation, the alternative is
to create your own Boost.Build project. A similar example you can use as
a starting point is available in <code><a href=
"../example/project.zip">this archive</a></code>. You'll need to edit the
Jamfile and Jamrules files, depending on the relative location of your
Boost installation and the new project. Note that automatic testing of
extension modules is not available in this configuration.
<h2><a name="variants">Build Variants</a></h2>
Three <a href=
"../../../tools/build/build_system.htm#variants">variant</a>
configurations of all python-related targets are supported, and can be
selected by setting the <code><a href=
"../../../tools/build/build_system.htm#user_globals">BUILD</a></code>
variable:
<ul>
<li><code>release</code> (optimization, <tt>-DNDEBUG</tt>)</li>
<li><code>debug</code> (no optimization <tt>-D_DEBUG</tt>)</li>
<li><code>debug-python</code> (no optimization, <tt>-D_DEBUG
-DBOOST_DEBUG_PYTHON</tt>)</li>
</ul>
<p>The first two variants of the <code>boost_python</code> library are
built by default, and are compatible with the default Python
distribution. The <code>debug-python</code> variant corresponds to a
specially-built debugging version of Python. On Unix platforms, this
python is built by adding <code>--with-pydebug</code> when configuring
the Python build. On Windows, the debugging version of Python is
generated by the "Win32 Debug" target of the <code>PCBuild.dsw</code>
Visual C++ 6.0 project in the <code>PCBuild</code> subdirectory of your
Python distribution. Extension modules built with Python debugging
enabled are <b>not link-compatible</b> with a non-debug build of Python.
Since few people actually have a debug build of Python (it doesn't come
with the standard distribution), the normal <code>debug</code> variant
builds modules which are compatible with ordinary Python.</p>
<p>On many windows compilers, when extension modules are built with
<tt>-D_DEBUG</tt>, Python defaults to <i>force</i> linking with a special
debugging version of the Python DLL. Since this debug DLL isn't supplied
with the default Python installation for Windows, Boost.Python uses
<tt><a href=
"../../../boost/python/detail/wrap_python.hpp">boost/python/detail/wrap_python.hpp</a></tt>
to temporarily undefine <tt>_DEBUG</tt> when <tt>Python.h</tt> is
<tt>#include</tt>d - unless <code>BOOST_DEBUG_PYTHON</code> is
defined.</p>
<p>If you want the extra runtime checks available with the debugging
version of the library, <tt>#define BOOST_DEBUG_PYTHON</tt> to re-enable
python debuggin, and link with the <code>debug-python</code> variant of
<tt>boost_python</tt>.</p>
<p>If you do not <tt>#define BOOST_DEBUG_PYTHON</tt>, be sure that any
source files in your extension module <tt>#include&nbsp;&lt;<a href=
"../../../boost/python/detail/wrap_python.hpp">boost/python/detail/wrap_python.hpp</a>&gt;</tt>
instead of the usual <tt>Python.h</tt>, or you will have link
incompatibilities.<br>
</p>
<hr>
<p>&copy; Copyright David Abrahams 2002. Permission to copy, use, modify,
sell and distribute this document is granted provided this copyright
notice appears in all copies. This document is provided ``as is'' without
express or implied warranty, and with no claim as to its suitability for
any purpose.</p>
<p>Updated: O8 October, 2002 (David Abrahams)</p>
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<h3><a href="../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Index</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="index">
<dt><a href="tutorial/index.html">Tutorial Introduction</a></dt>
<dt><a href="building.html">Building and Testing</a></dt>
<dt><a href="v2/reference.html">Reference</a></dt>
<dt><a href="v2/configuration.html">Configuration Information</a></dt>
<dt><a href="v2/rationale.html">Rationale</a></dt>
<dt><a href="v2/definitions.html">Definitions</a></dt>
<dt><a href="v2/faq.html">Frequently Asked Questions (FAQs)</a></dt>
<dt><a href="v2/progress_reports.html">Progress Reports</a></dt>
<dt><a href="v2/acknowledgments.html">Acknowledgments</a></dt>
</dl>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
08 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i></p>
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<title>A New Type Conversion Mechanism for Boost.Python</title>
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<h1>A New Type Conversion Mechanism for Boost.Python</h1>
<p>By <a href="../../../people/dave_abrahams.htm">David Abrahams</a>.
<h2>Introduction</h2>
This document describes a redesign of the mechanism for automatically
converting objects between C++ and Python. The current implementation
uses two functions for any type <tt>T</tt>:
<blockquote><pre>
U from_python(PyObject*, type&lt;T&gt;);
void to_python(V);
</pre></blockquote>
where U is convertible to T and T is convertible to V. These functions
are at the heart of C++/Python interoperability in Boost.Python, so
why would we want to change them? There are many reasons:
<h3>Bugs</h3>
<p>Firstly, the current mechanism relies on a common C++ compiler
bug. This is not just embarrassing: as compilers get to be more
conformant, the library stops working. The issue, in detail, is the
use of inline friend functions in templates to generate
conversions. It is a very powerful, and legal technique as long as
it's used correctly:
<blockquote><pre>
template &lt;class Derived&gt;
struct add_some_functions
{
friend <i>return-type</i> some_function1(..., Derived <i>cv-*-&amp;-opt</i>, ...);
friend <i>return-type</i> some_function2(..., Derived <i>cv-*-&amp;-opt</i>, ...);
};
template &lt;class T&gt;
struct some_template : add_some_functions&lt;some_template&lt;T&gt; &gt;
{
};
</pre></blockquote>
The <tt>add_some_functions</tt> template generates free functions
which operate on <tt>Derived</tt>, or on related types. Strictly
speaking the related types are not just cv-qualified <tt>Derived</tt>
values, pointers and/or references. Section 3.4.2 in the standard
describes exactly which types you must use as parameters to these
functions if you want the functions to be found
(there is also a less-technical description in section 11.5.1 of
C++PL3 <a href="#ref_1">[1]</a>). Suffice it to say that
with the current design, the <tt>from_python</tt> and
<tt>to_python</tt> functions are not supposed to be callable under any
conditions!
<h3>Compilation and Linking Time</h3>
The conversion functions generated for each wrapped class using the
above technique are not function templates, but regular functions. The
upshot is that they must <i>all</i> be generated regardless of whether
they are actually used. Generating all of those functions can slow
down module compilation, and resolving the references can slow down
linking.
<h3>Efficiency</h3>
The conversion functions are primarily used in (member) function
wrappers to convert the arguments and return values. Being functions,
converters have no interface which allows us to ask &quot;will the
conversion succeed?&quot; without calling the function. Since the
return value of the function must be the object to be passed as an
argument, Boost.Python currently uses C++ exception-handling to detect
an unsuccessful conversion. It's not a particularly good use of
exception-handling, since the failure is not handled very far from
where it occurred. More importantly, it means that C++ exceptions are
thrown during overload resolution as we seek an overload that matches
the arguments passed. Depending on the implementation, this approach
can result in significant slowdowns.
<p>It is also unclear that the current library generates a minimal
amount of code for any type conversion. Many of the conversion
functions are nontrivial, and partly because of compiler limitations,
they are declared <tt>inline</tt>. Also, we could have done a better
job separating the type-specific conversion code from the code which
is type-independent.
<h3>Cross-module Support</h3>
The current strategy requires every module to contain the definition
of conversions it uses. In general, a new module can never supply
conversion code which is used by another module. Ralf Grosse-Kunstleve
designed a clever system which imports conversions directly from one
library into another using some explicit declarations, but it has some
disadvantages also:
<ol>
<li>The system Ullrich Koethe designed for implicit conversion between
wrapped classes related through inheritance does not currently work if
the classes are defined in separate modules.
<li>The writer of the importing module is required to know the name of
the module supplying the imported conversions.
<li>There can be only one way to extract any given C++ type from a
Python object in a given module.
</ol>
The first item might be addressed by moving Boost.Python into a shared
library, but the other two cannot. Ralf turned the limitation in item
two into a feature: the required module is loaded implicitly when a
conversion it defines is invoked. We will probably want to provide
that functionality anyway, but it's not clear that we should require
the declaration of all such conversions. The final item is a more
serious limitation. If, for example, new numeric types are defined in
separate modules, and these types can all be converted to
<tt>double</tt>s, we have to choose just one conversion method.
<h3>Ease-of-use</h3>
One persistent source of confusion for users of Boost.Python has been
the fact that conversions for a class are not be visible at
compile-time until the declaration of that class has been seen. When
the user tries to expose a (member) function operating on or returning
an instance of the class in question, compilation fails...even though
the user goes on to expose the class in the same translation unit!
<p>
The new system lifts all compile-time checks for the existence of
particular type conversions and replaces them with runtime checks, in
true Pythonic style. While this might seem cavalier, the compile-time
checks are actually not much use in the current system if many classes
are wrapped in separate modules, since the checks are based only on
the user's declaration that the conversions exist.
<h2>The New Design</h2>
<h3>Motivation</h3>
The new design was heavily influenced by a desire to generate as
little code as possible in extension modules. Some of Boost.Python's
clients are enormous projects where link time is proportional to the
amount of object code, and there are many Python extension modules. As
such, we try to keep type-specific conversion code out of modules
other than the one the converters are defined in, and rely as much as
possible on centralized control through a shared library.
<h3>The Basics</h3>
The library contains a <tt>registry</tt> which maps runtime type
identifiers (actually an extension of <tt>std::type_info</tt> which
preserves references and constness) to entries containing type
converters. An <tt>entry</tt> can contain only one converter from C++ to Python
(<tt>wrapper</tt>), but many converters from Python to C++
(<tt>unwrapper</tt>s). <font color="#ff0000">What should happen if
multiple modules try to register wrappers for the same type?</font>. Wrappers
and unwrappers are known as <tt>body</tt> objects, and are accessed
by the user and the library (in its function-wrapping code) through
corresponding <tt>handle</tt> (<tt>wrap&lt;T&gt;</tt> and
<tt>unwrap&lt;T&gt;</tt>) objects. The <tt>handle</tt> objects are
extremely lightweight, and delegate <i>all</i> of their operations to
the corresponding <tt>body</tt>.
<p>
When a <tt>handle</tt> object is constructed, it accesses the
registry to find a corresponding <tt>body</tt> that can convert the
handle's constructor argument. Actually the registry record for any
type
<tt>T</tt>used in a module is looked up only once and stored in a
static <tt>registration&lt;T&gt;</tt> object for efficiency. For
example, if the handle is an <tt>unwrap&lt;Foo&amp;&gt;</tt> object,
the <tt>entry</tt> for <tt>Foo&amp;</tt> is looked up in the
<tt>registry</tt>, and each <tt>unwrapper</tt> it contains is queried
to determine if it can convert the
<tt>PyObject*</tt> with which the <tt>unwrap</tt> was constructed. If
a body object which can perform the conversion is found, a pointer to
it is stored in the handle. A body object may at any point store
additional data in the handle to speed up the conversion process.
<p>
Now that the handle has been constructed, the user can ask it whether
the conversion can be performed. All handles can be tested as though
they were convertible to <tt>bool</tt>; a <tt>true</tt> value
indicates success. If the user forges ahead and tries to do the
conversion without checking when no conversion is possible, an
exception will be thrown as usual. The conversion itself is performed
by the body object.
<h3>Handling complex conversions</h3>
<p>Some conversions may require a dynamic allocation. For example,
when a Python tuple is converted to a <tt>std::vector&lt;double&gt;
const&amp;</tt>, we need some storage into which to construct the
vector so that a reference to it can be formed. Furthermore, multiple
conversions of the same type may need to be &quot;active&quot;
simultaneously, so we can't keep a single copy of the storage
anywhere. We could keep the storage in the <tt>body</tt> object, and
have the body clone itself in case the storage is used, but in that
case the storage in the body which lives in the registry is never
used. If the storage was actually an object of the target type (the
safest way in C++), we'd have to find a way to construct one for the
body in the registry, since it may not have a default constructor.
<p>
The most obvious way out of this quagmire is to allocate the object using a
<i>new-expression</i>, and store a pointer to it in the handle. Since
the <tt>body</tt> object knows everything about the data it needs to
allocate (if any), it is also given responsibility for destroying that
data. When the <tt>handle</tt> is destroyed it asks the <tt>body</tt>
object to tear down any data it may have stored there. In many ways,
you can think of the <tt>body</tt> as a &quot;dynamically-determined
vtable&quot; for the handle.
<h3>Eliminating Redundancy</h3>
If you look at the current Boost.Python code, you'll see that there
are an enormous number of conversion functions generated for each
wrapped class. For a given class <tt>T</tt>, functions are generated
to extract the following types <tt>from_python</tt>:
<blockquote><pre>
T*
T const*
T const* const&amp;
T* const&amp;
T&amp;
T const&amp;
T
std::auto_ptr&lt;T&gt;&amp;
std::auto_ptr&lt;T&gt;
std::auto_ptr&lt;T&gt; const&amp;
boost::shared_ptr&lt;T&gt;&amp;
boost::shared_ptr&lt;T&gt;
boost::shared_ptr&lt;T&gt; const&amp;
</pre></blockquote>
Most of these are implemented in terms of just a few conversions, and
<t>if you're lucky</t>, they will be inlined and cause no extra
overhead. In the new system, however, a significant amount of data
will be associated with each type that needs to be converted. We
certainly don't want to register a separate unwrapper object for all
of the above types.
<p>Fortunately, much of the redundancy can be eliminated. For example,
if we generate an unwrapper for <tt>T&</tt>, we don't need an
unwrapper for <tt>T const&</tt> or <tt>T</tt>. Accordingly, the user's
request to wrap/unwrap a given type is translated at compile-time into
a request which helps to eliminate redundancy. The rules used to
<tt>unwrap</tt> a type are:
<ol>
<li> Treat built-in types specially: when unwrapping a value or
constant reference to one of these, use a value for the target
type. It will bind to a const reference if neccessary, and more
importantly, avoids having to dynamically allocate room for
an lvalue of types which can be cheaply copied.
<li>
Reduce everything else to a reference to an un-cv-qualified type
where possible. Since cv-qualification is lost on Python
anyway, there's no point in trying to convert to a
<tt>const&amp;</tt>. <font color="#ff0000">What about conversions
to values like the tuple-&gt;vector example above? It seems to me
that we don't want to make a <tt>vector&lt;double&gt;&amp;</tt>
(non-const) converter available for that case. We may need to
rethink this slightly.</font>
</ol>
<p>To handle the problem described above in item 2, we modify the
procedure slightly. To unwrap any non-scalar <tt>T</tt>, we seek an
unwrapper for <tt>add_reference&lt;T&gt;::type</tt>. Unwrappers for
<tt>T&nbsp;const&amp;</tt> always return <tt>T&amp;</tt>, and are
registered under both <tt>T&nbsp;&amp;</tt> and
<tt>T&nbsp;const&amp;</tt>.
<p>For compilers not supporting partial specialization, unwrappers for
<tt>T&nbsp;const&amp;</tt> must return <tt>T&nbsp;const&amp;</tt>
(since constness can't be stripped), but a separate unwrapper object
need to be registered for <tt>T&nbsp;&amp;</tt> and
<tt>T&nbsp;const&amp;</tt> anyway, for the same reasons.
<font color="#ff0000">We may want to make it possible to compile as
though partial specialization were unavailable even on compilers where
it is available, in case modules could be compiled by different
compilers with compatible ABIs (e.g. Intel C++ and MSVC6).</font>
<h3>Efficient Argument Conversion</h3>
Since type conversions are primarily used in function wrappers, an
optimization is provided for the case where a group of conversions are
used together. Each <tt>handle</tt> class has a corresponding
&quot;<tt>_more</tt>&quot; class which does the same job, but has a
trivial destructor. Instead of asking each &quot;<tt>_more</tt>&quot;
handle to destroy its own body, it is linked into an endogenous list
managed by the first (ordinary) handle. The <tt>wrap</tt> and
<tt>unwrap</tt> destructors are responsible for traversing that list
and asking each <tt>body</tt> class to tear down its
<tt>handle</tt>. This mechanism is also used to determine if all of
the argument/return-value conversions can succeed with a single
function call in the function wrapping code. <font color="#ff0000">We
might need to handle return values in a separate step for Python
callbacks, since the availablility of a conversion won't be known
until the result object is retrieved.</font>
<br>
<hr>
<h2>References</h2>
<p><a name="ref_1">[1]</a>B. Stroustrup, The C++ Programming Language
Special Edition Addison-Wesley, ISBN 0-201-70073-5.
<hr>
<p>Revised <!--webbot bot="Timestamp" s-type="EDITED" s-format="%d %B %Y" startspan -->19 December 2001<!--webbot bot="Timestamp" endspan i-checksum="31283" --></p>
<p>© Copyright David Abrahams, 2001</p>
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This hierarchy contains converter handle classes.
+-------------+
| noncopyable |
+-------------+
^
| A common base class used so that
+--------+--------+ conversions can be linked into a
| conversion_base | chain for efficient argument
+-----------------+ conversion
^
|
+---------+-----------+
| |
+-----------+----+ +------+-------+ only used for
| unwrap_more<T> | | wrap_more<T> | chaining, and don't manage any
+----------------+ +--------------+ resources.
^ ^
| |
+-----+-----+ +-------+-+ These converters are what users
| unwrap<T> | | wrap<T> | actually touch, but they do so
+-----------+ +---------+ through a type generator which
minimizes the number of converters
that must be generated, so they
Each unwrap<T>, unwrap_more<T>, wrap<T>, wrap_more<T> converter holds
a reference to an appropriate converter object
This hierarchy contains converter body classes
Exposes use/release which
are needed in case the converter
+-----------+ in the registry needs to be
| converter | cloned. That occurs when a
+-----------+ unwrap target type is not
^ contained within the Python object.
|
+------------------+-----+
| |
+--------+-------+ Exposes |
| unwrapper_base | convertible() |
+----------------+ |
^ |
| |
+--------+----+ +-----+-----+
| unwrapper<T>| | wrapper<T>|
+-------------+ +-----------+
Exposes T convert(PyObject*) Exposes PyObject* convert(T)
unwrap:
constructed with a PyObject*, whose reference count is
incremented.
find the registry entry for the target type
look in the collection of converters for one which claims to be
able to convert the PyObject to the target type.
stick a pointer to the unwrapper in the unwrap object
when unwrap is queried for convertibility, it checks to see
if it has a pointer to an unwrapper.
on conversion, the unwrapper is asked to allocate an
implementation if the unwrap object isn't already holding
one. The unwrap object "takes ownership" of the unwrapper's
implementation. No memory allocation will actually take place
unless this is a value conversion.
on destruction, the unwrapper is asked to free any implementation
held by the unwrap object. No memory deallocation actually
takes place unless this is a value conversion
on destruction, the reference count on the held PyObject is
decremented.
We need to make sure that by default, you can't instantiate
callback<> for reference and pointer return types: although the
unwrappers may exist, they may convert by-value, which would cause
the referent to be destroyed upon return.
wrap:
find the registry entry for the source type
see if there is a converter. If found, stick a pointer to it in
the wrap object.
when queried for convertibility, it checks to see if it has a
pointer to a converter.
on conversion, a reference to the target PyObject is held by the
converter. Generally, the PyObject will have been created by the
converter, but in certain cases it may be a pre-existing object,
whose reference count will have been incremented.
when a wrap<T> x is used to return from a C++ function,
x.release() is returned so that x no longer holds a reference to
the PyObject when destroyed.
Otherwise, on destruction, any PyObject still held has its
reference-count decremented.
When a converter is created by the user, the appropriate element must
be added to the registry; when it is destroyed, it must be removed
from the registry.

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<html>
<head>
<!-- Generated by the Spirit (http://spirit.sf.net) QuickDoc -->
<title>Basic Interface</title>
<link rel="stylesheet" href="theme/style.css" type="text/css">
<link rel="prev" href="object_interface.html">
<link rel="next" href="derived_object_types.html">
</head>
<body>
<table width="100%" height="48" border="0" cellspacing="2">
<tr>
<td><img src="theme/c%2B%2Bboost.gif">
</td>
<td width="85%">
<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Basic Interface</b></font>
</td>
</tr>
</table>
<br>
<table border="0">
<tr>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
<td width="30"><a href="object_interface.html"><img src="theme/l_arr.gif" border="0"></a></td>
<td width="20"><a href="derived_object_types.html"><img src="theme/r_arr.gif" border="0"></a></td>
</tr>
</table>
<p>
Class <tt>object</tt> wraps <tt>PyObject*</tt>. All the intricacies of dealing with
<tt>PyObject</tt>s such as managing reference counting are handled by the
<tt>object</tt> class. C++ object interoperability is seamless. Boost.Python C++
<tt>object</tt>s can in fact be explicitly constructed from any C++ object.</p>
<p>
To illustrate, this Python code snippet:</p>
<code><pre>
<span class=identifier>def </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>x</span><span class=special>, </span><span class=identifier>y</span><span class=special>):
</span><span class=keyword>if </span><span class=special>(</span><span class=identifier>y </span><span class=special>== </span><span class=literal>'foo'</span><span class=special>):
</span><span class=identifier>x</span><span class=special>[</span><span class=number>3</span><span class=special>:</span><span class=number>7</span><span class=special>] </span><span class=special>= </span><span class=literal>'bar'
</span><span class=keyword>else</span><span class=special>:
</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>items </span><span class=special>+= </span><span class=identifier>y</span><span class=special>(</span><span class=number>3</span><span class=special>, </span><span class=identifier>x</span><span class=special>)
</span><span class=keyword>return </span><span class=identifier>x
</span><span class=identifier>def </span><span class=identifier>getfunc</span><span class=special>():
</span><span class=keyword>return </span><span class=identifier>f</span><span class=special>;
</span></pre></code>
<p>
Can be rewritten in C++ using Boost.Python facilities this way:</p>
<code><pre>
<span class=identifier>object </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>object </span><span class=identifier>x</span><span class=special>, </span><span class=identifier>object </span><span class=identifier>y</span><span class=special>) </span><span class=special>{
</span><span class=keyword>if </span><span class=special>(</span><span class=identifier>y </span><span class=special>== </span><span class=string>&quot;foo&quot;</span><span class=special>)
</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>slice</span><span class=special>(</span><span class=number>3</span><span class=special>,</span><span class=number>7</span><span class=special>) </span><span class=special>= </span><span class=string>&quot;bar&quot;</span><span class=special>;
</span><span class=keyword>else
</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>attr</span><span class=special>(</span><span class=string>&quot;items&quot;</span><span class=special>) </span><span class=special>+= </span><span class=identifier>y</span><span class=special>(</span><span class=number>3</span><span class=special>, </span><span class=identifier>x</span><span class=special>);
</span><span class=keyword>return </span><span class=identifier>x</span><span class=special>;
</span><span class=special>}
</span><span class=identifier>object </span><span class=identifier>getfunc</span><span class=special>() </span><span class=special>{
</span><span class=keyword>return </span><span class=identifier>object</span><span class=special>(</span><span class=identifier>f</span><span class=special>);
</span><span class=special>}
</span></pre></code>
<p>
Apart from cosmetic differences due to the fact that we are writing the
code in C++, the look and feel should be immediately apparent to the Python
coder.</p>
<table border="0">
<tr>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
<td width="30"><a href="object_interface.html"><img src="theme/l_arr.gif" border="0"></a></td>
<td width="20"><a href="derived_object_types.html"><img src="theme/r_arr.gif" border="0"></a></td>
</tr>
</table>
<br>
<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
is granted provided this copyright notice appears in all copies. This document
is provided &quot;as is&quot; without express or implied warranty, and with
no claim as to its suitability for any purpose. </font> </p>
</body>
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<html>
<head>
<!-- Generated by the Spirit (http://spirit.sf.net) QuickDoc -->
<title>Building an Extension Module </title>
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<td><img src="theme/c%2B%2Bboost.gif">
</td>
<td width="85%"> <font size="6" face="Verdana, Arial, Helvetica, sans-serif"><strong>Building
an Extension Module</strong></font> </td>
</tr>
</table>
<br>
<table border="0">
<tr>
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<td width="30"><img src="theme/l_arr.gif" border="0"></td>
<td width="20"><img src="theme/r_arr.gif" border="0"></td>
</tr>
</table>
<h2>Building Boost.Python</h2>
<p>Every Boost.Python extension module must be linked with the boost_python shared
library. To build boost_python, use <a href="file:///C:/dev/boost/tools/build/index.html">Boost.Build</a>
in the usual way from the <tt>libs/python/build</tt> subdirectory of your boost
installation (if you have already built boost from the top level this may have
no effect, since the work is already done).</p>
<h2>Configuration</h2>
<p>You may need to configure the following variables to point Boost.Build at your
Python installation:</p>
<table width="95%" border="0" align="center">
<tr class="table_title">
<td width="24%">Variable Name</td>
<td width="20%">Semantics</td>
<td width="21%">Default</td>
<td width="35%">Notes</td>
</tr>
<tr class="table_cells">
<td><tt>PYTHON_ROOT</tt></td>
<td> The root directory of your Python installation</td>
<td>Windows: <tt><br>
c:/tools/python <br>
Unix: /usr/local</tt></td>
<td>On Unix, this is the <tt>--with-prefix=</tt> directory used to configure
Python</td>
</tr>
<tr class="table_cells">
<td><tt>PYTHON_VERSION</tt></td>
<td> The The 2-part python Major.Minor version number</td>
<td>Windows: 2.1 Unix: 1.5</td>
<td>Be sure not to include a third number, e.g. not &quot;2.2.1&quot;, even
if that's the version you have.</td>
</tr>
<tr class="table_cells">
<td><tt>PYTHON_INCLUDES</tt></td>
<td> path to Python <span class="preprocessor">#include</span> directories</td>
<td>Autoconfigured from <tt><br>
PYTHON_ROOT</tt></td>
<td>&nbsp;</td>
</tr>
<tr class="table_cells">
<td><tt>PYTHON_LIB_PATH</tt></td>
<td>path to Python library object.</td>
<td>Autoconfigured from <tt><br>
PYTHON_ROOT</tt></td>
<td>&nbsp;</td>
</tr>
<tr class="table_cells">
<td><tt>PYTHON_STDLIB_PATH</tt></td>
<td>path to Python standard library modules</td>
<td>Autoconfigured from <tt><br>
PYTHON_ROOT</tt></td>
<td>&nbsp;</td>
</tr>
<tr class="table_cells">
<td height="129"><tt>CYGWIN_ROOT</tt></td>
<td> path to the user's Cygwin installation</td>
<td>Autoconfigured from <tt><br>
PYTHON_ROOT</tt></td>
<td><a href="http://www.cygwin.com">Cygwin</a> only. This and the following
two settings are useful when building with multiple toolsets on Windows,
since Cygwin requires a different build of Python.</td>
</tr>
<tr class="table_cells">
<td height="21"><tt>GCC_PYTHON_ROOT</tt></td>
<td>path to the user's Cygwin Python installation</td>
<td><tt>$(CYGWIN_ROOT)<br>
/usr/local</tt></td>
<td> <a href="http://www.cygwin.com">Cygwin</a> only</td>
</tr>
<tr class="table_cells">
<td><tt>GCC_DEBUG_PYTHON_ROOT</tt></td>
<td> path to the user's Cygwin <a href="#variants">pydebug</a>
build</td>
<td><tt>$(CYGWIN_ROOT)<br>
/usr/local/pydebug</tt></td>
<td> <a href="http://www.cygwin.com">Cygwin</a> only</td>
</tr>
</table>
<h2>Results</h2>
<p>The build process will create a <tt>libs/python/build/bin-stage</tt> subdirectory
of the boost root (or of <tt>$(ALL_LOCATE_TARGET)</tt>, if you have set that
variable), containing the built libraries. The libraries are actually built
to unique directories for each toolset and variant elsewhere in the filesystem,
and copied to the bin-stage directory as a convenience, so if you build with
multiple toolsets at once, the product of later toolsets will overwrite that
of earlier toolsets in bin-stage.</p>
<h2>Testing</h2>
<p>To build and test Boost.Python from within the <tt>libs/python/build directory</tt>,
invoke</p>
<pre> bjam -sTOOLS=<a href="../../../tools/build/index.html">toolset</a> test</pre>
<p>This will update all of the Boost.Python v1 test and example targets. The tests
are relatively quiet by default. To get more-verbose output, you might try</p>
<pre> bjam -sTOOLS=<a href="../../../tools/build/index.html">toolset</a> -sPYTHON_TEST_ARGS=-v test</pre>
<p>which will print each test's Python code with the expected output as it passes.</p>
<h2>Building your Extension Module</h2>
<p>Though there are other approaches, the easiest way to build an extension module
using Boost.Python is with Boost.Build. Until Boost.Build v2 is released, cross-project
build dependencies are not supported, so it works most smoothly if you add a
new subproject to your boost installation. The <tt>libs/python/example</tt>
subdirectory of your boost installation contains a minimal example (along with
many extra sources). To copy the example subproject:</p>
<ol>
<li> Create a new subdirectory in,<tt> libs/python</tt>, say <tt>libs/python/my_project</tt>.</li>
<li> Copy <a href="../example/Jamfile"><tt>libs/python/example/Jamfile</tt></a>
to your new directory.</li>
<li> Edit the Jamfile as appropriate for your project. You'll want to change
the <tt>subproject</tt> rule invocation at the top, and the names of some
of the source files and/or targets.</li>
</ol>
<p>If you can't modify or copy your boost installation, the alternative is to
create your own Boost.Build project. A similar example you can use as a starting
point is available in <a href="../example/project.zip">this archive</a>. You'll
need to edit the Jamfile and Jamrules files, depending on the relative location
of your Boost installation and the new project. Note that automatic testing
of extension modules is not available in this configuration.</p>
<h2>Build Variants</h2>
<p>Three variant configurations of all python-related targets are supported, and
can be selected by setting the BUILD variable:</p>
<p> * <tt>release</tt> (optimization, <tt>-DNDEBUG</tt>)<br>
* <tt>debug</tt> (no optimization <tt>-D_DEBUG</tt>)<br>
* <tt>debug-python</tt> (no optimization, <tt>-D_DEBUG -DBOOST_DEBUG_PYTHON</tt>)</p>
<p>The first two variants of the boost_python library are built by default, and
are compatible with the default Python distribution. The debug-python variant
corresponds to a specially-built debugging version of Python. On Unix platforms,
this python is built by adding <tt>--with-pydebug</tt> when configuring the
Python build. On Windows, the debugging version of Python is generated by the
&quot;Win32 Debug&quot; target of the PCBuild.dsw Visual C++ 6.0 project in
the PCBuild subdirectory of your Python distribution. Extension modules built
with Python debugging enabled are not link-compatible with a non-debug build
of Python. Since few people actually have a debug build of Python (it doesn't
come with the standard distribution), the normal debug variant builds modules
which are compatible with ordinary Python.</p>
<p>On many windows compilers, when extension modules are built with <tt>-D_DEBUG</tt>,
Python defaults to force linking with a special debugging version of the Python
DLL. Since this debug DLL isn't supplied with the default Python installation
for Windows, Boost.Python uses <a href="../../../boost/python/detail/wrap_python.hpp"><tt>boost/python/detail/wrap_python.hpp</tt></a>
to temporarily undefine <tt>_DEBUG</tt> when <tt>Python.h</tt> is <span class="preprocessor">#included</span>
- unless <tt>BOOST_DEBUG_PYTHON</tt> is defined.</p>
<p>If you want the extra runtime checks available with the debugging version of
the library, <span class="preprocessor">#define</span> <tt>BOOST_DEBUG_PYTHON</tt>
to re-enable python debuggin, and link with the debug-python variant of boost_python.</p>
<p>If you do not <span class="preprocessor">#define</span> <tt>BOOST_DEBUG_PYTHON</tt>,
be sure that any source files in your extension module <span class="preprocessor">#include</span>
<tt>&lt;boost/python/detail/wrap_python.hpp&gt;</tt> instead of the usual <tt>Python.h</tt>,
or you will have link incompatibilities.</p>
<code></code>
<table border="0">
<tr>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
<td width="30"><img src="theme/l_arr.gif" border="0"></td>
<td width="20"><img src="theme/r_arr.gif" border="0"></td>
</tr>
</table>
<br>
<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
is granted provided this copyright notice appears in all copies. This document
is provided &quot;as is&quot; without express or implied warranty, and with
no claim as to its suitability for any purpose. </font> </p>
</body>
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<html>
<head>
<!-- Generated by the Spirit (http://spirit.sf.net) QuickDoc -->
<title>Building Hello World</title>
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<td><img src="theme/c%2B%2Bboost.gif">
</td>
<td width="85%">
<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Building Hello World</b></font>
</td>
</tr>
</table>
<br>
<table border="0">
<tr>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
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</tr>
</table>
<a name="from_start_to_finish"></a><h2>From Start To Finish</h2><p>
Now the first thing you'd want to do is to build the Hello World module and
try it for yourself in Python. In this section, we shall outline the steps
necessary to achieve that. We shall use the build tool that comes bundled
with every boost distribution: <b>bjam</b>.</p>
<table width="80%" border="0" align="center">
<tr>
<td class="note_box">
<img src="theme/lens.gif"></img> <b>Building without bjam</b><br><br>
Besides bjam, there are of course other ways to get your module built.
What's written here should not be taken as &quot;the one and only way&quot;.
There are of course other build tools apart from <tt>bjam</tt>.
</td>
</tr>
</table>
<p>
We shall skip over the details. Our objective will be to simply create the
hello world module and run it in Python. For a complete reference to
building Boost.Python, check out: <a href="../../building.html">
building.html</a>.
After this brief <i>bjam</i> tutorial, we should have built two DLLs:</p>
<ul><li>boost_python.dll</li><li>hello.pyd</li></ul><p>
if you are on Windows, and</p>
<ul><li>libboost_python.so</li><li>hello.so</li></ul><p>
if you are on Unix.</p>
<p>
The tutorial example can be found in the directory:
<tt>libs/python/example/tutorial</tt>. There, you can find:</p>
<ul><li>hello.cpp</li><li>Jamfile</li></ul><p>
The <tt>hello.cpp</tt> file is our C++ hello world example. The <tt>Jamfile</tt> is a
minimalist <i>bjam</i> script that builds the DLLs for us.</p>
<p>
Before anything else, you should have the bjam executable in your boost
directory or somewhere in your path such that <tt>bjam</tt> can be executed in
the command line. Pre-built Boost.Jam executables are available for most
platforms. For example, a pre-built Microsoft Windows bjam executable can
be downloaded <a href="http://boost.sourceforge.net/jam-executables/bin.ntx86/bjam.zip">
here</a>.
The complete list of bjam pre-built
executables can be found <a href="../../../../../tools/build/index.html#Jam">
here</a>.</p>
<a name="lets_jam_"></a><h2>Lets Jam!</h2><p>
<img src="theme/jam.png"></img></p>
<p>
Here is our minimalist Jamfile:</p>
<code><pre>
subproject libs/python/example/tutorial ;
SEARCH on python.jam = $(BOOST_BUILD_PATH) ;
include python.jam ;
extension hello # Declare a Python extension called hello
: hello.cpp # source
&lt;dll&gt;../../build/boost_python # dependencies
;
</pre></code><p>
First, we need to specify our location in the boost project hierarchy.
It so happens that the tutorial example is located in <tt>/libs/python/example/tutorial</tt>.
Thus:</p>
<code><pre>
subproject libs/python/example/tutorial ;
</pre></code><p>
Then we will include the definitions needed by Python modules:</p>
<code><pre>
SEARCH on python.jam = $(BOOST_BUILD_PATH) ;
include python.jam ;
</pre></code><p>
Finally we declare our <tt>hello</tt> extension:</p>
<code><pre>
extension hello # Declare a Python extension called hello
: hello.cpp # source
&lt;dll&gt;../../build/boost_python # dependencies
;
</pre></code><a name="running_bjam"></a><h2>Running bjam</h2><p>
<i>bjam</i> is run using your operating system's command line interpreter.</p>
<blockquote><p>Start it up.</p></blockquote><p>
Make sure that the environment is set so that we can invoke the C++
compiler. With MSVC, that would mean running the <tt>Vcvars32.bat</tt> batch
file. For instance:</p>
<code><pre>
<span class=identifier>C</span><span class=special>:\</span><span class=identifier>Program </span><span class=identifier>Files</span><span class=special>\</span><span class=identifier>Microsoft </span><span class=identifier>Visual </span><span class=identifier>Studio</span><span class=special>\</span><span class=identifier>VC98</span><span class=special>\</span><span class=identifier>bin</span><span class=special>\</span><span class=identifier>Vcvars32</span><span class=special>.</span><span class=identifier>bat
</span></pre></code>
<p>
Some environment variables will have to be setup for proper building of our
Python modules. Example:</p>
<code><pre>
<span class=identifier>set </span><span class=identifier>PYTHON_ROOT</span><span class=special>=</span><span class=identifier>c</span><span class=special>:/</span><span class=identifier>dev</span><span class=special>/</span><span class=identifier>tools</span><span class=special>/</span><span class=identifier>python
</span><span class=identifier>set </span><span class=identifier>PYTHON_VERSION</span><span class=special>=</span><span class=number>2.2
</span></pre></code>
<p>
The above assumes that the Python installation is in <tt>c:/dev/tools/python</tt>
and that we are using Python version 2.2. You'll have to tweak this path
appropriately. <img src="theme/note.gif"></img> Be sure not to include a third number, e.g. <b>not</b> &quot;2.2.1&quot;,
even if that's the version you have.</p>
<p>
Now we are ready... Be sure to <tt>cd</tt> to <tt>libs/python/example/tutorial</tt>
where the tutorial <tt>&quot;hello.cpp&quot;</tt> and the <tt>&quot;Jamfile&quot;</tt> is situated.</p>
<p>
Finally:</p>
<code><pre>
<span class=identifier>bjam </span><span class=special>-</span><span class=identifier>sTOOLS</span><span class=special>=</span><span class=identifier>msvc
</span></pre></code>
<p>
We are again assuming that we are using Microsoft Visual C++ version 6. If
not, then you will have to specify the appropriate tool. See
<a href="../../../../../tools/build/index.html">
Building Boost Libraries</a> for
further details.</p>
<p>
It should be building now:</p>
<code><pre>
cd C:\dev\boost\libs\python\example\tutorial
bjam -sTOOLS=msvc
...patience...
...found 1703 targets...
...updating 40 targets...
</pre></code><p>
And so on... Finally:</p>
<code><pre>
vc-C++ ..\..\..\..\libs\python\example\tutorial\bin\hello.pyd\msvc\debug\
runtime-link-dynamic\hello.obj
hello.cpp
vc-Link ..\..\..\..\libs\python\example\tutorial\bin\hello.pyd\msvc\debug\
runtime-link-dynamic\hello.pyd ..\..\..\..\libs\python\example\tutorial\bin\
hello.pyd\msvc\debug\runtime-link-dynamic\hello.lib
Creating library ..\..\..\..\libs\python\example\tutorial\bin\hello.pyd\
msvc\debug\runtime-link-dynamic\hello.lib and object ..\..\..\..\libs\python\
example\tutorial\bin\hello.pyd\msvc\debug\runtime-link-dynamic\hello.exp
...updated 40 targets...
</pre></code><p>
If all is well, you should now have:</p>
<ul><li>boost_python.dll</li><li>hello.pyd</li></ul><p>
if you are on Windows, and</p>
<ul><li>libboost_python.so</li><li>hello.so</li></ul><p>
if you are on Unix.</p>
<p>
<tt>boost_python.dll</tt> can be found somewhere in <tt>libs\python\build\bin</tt>
while <tt>hello.pyd</tt> can be found somewhere in
<tt>libs\python\example\tutorial\bin</tt>. After a successful build, you can just
link in these DLLs with the Python interpreter. In Windows for example, you
can simply put these libraries inside the directory where the Python
executable is.</p>
<p>
You may now fire up Python and run our hello module:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>import </span><span class=identifier>hello
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>print </span><span class=identifier>hello</span><span class=special>.</span><span class=identifier>greet</span><span class=special>()
</span><span class=identifier>hello</span><span class=special>, </span><span class=identifier>world
</span></pre></code>
<blockquote><p><b>There you go... Have fun!</b></p></blockquote><table border="0">
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<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
is granted provided this copyright notice appears in all copies. This document
is provided &quot;as is&quot; without express or implied warranty, and with
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<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Call Policies</b></font>
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<p>
In C++, we often deal with arguments and return types such as pointers
and references. Such primitive types are rather, ummmm, low level and
they really don't tell us much. At the very least, we don't know the
owner of the pointer or the referenced object. No wonder languages
such as Java and Python never deal with such low level entities. In
C++, it's usually considered a good practice to use smart pointers
which exactly describe ownership semantics. Still, even good C++
interfaces use raw references and pointers sometimes, so Boost.Python
must deal with them. To do this, it may need your help. Consider the
following C++ function:</p>
<code><pre>
<span class=identifier>X</span><span class=special>&amp; </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>Y</span><span class=special>&amp; </span><span class=identifier>y</span><span class=special>, </span><span class=identifier>Z</span><span class=special>* </span><span class=identifier>z</span><span class=special>);
</span></pre></code>
<p>
How should the library wrap this function? A naive approach builds a
Python X object around result reference. This strategy might or might
not work out. Here's an example where it didn't</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>x </span><span class=special>= </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>y</span><span class=special>, </span><span class=identifier>z</span><span class=special>) </span>#<span class=identifier>x </span><span class=identifier>refers </span><span class=identifier>to </span><span class=identifier>some </span><span class=identifier>C</span><span class=special>++ </span><span class=identifier>X
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>del </span><span class=identifier>y
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>some_method</span><span class=special>() </span>#<span class=identifier>CRASH</span><span class=special>!
</span></pre></code>
<p>
What's the problem?</p>
<p>
Well, what if f() was implemented as shown below:</p>
<code><pre>
<span class=identifier>X</span><span class=special>&amp; </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>Y</span><span class=special>&amp; </span><span class=identifier>y</span><span class=special>, </span><span class=identifier>Z</span><span class=special>* </span><span class=identifier>z</span><span class=special>)
</span><span class=special>{
</span><span class=identifier>y</span><span class=special>.</span><span class=identifier>z </span><span class=special>= </span><span class=identifier>z</span><span class=special>;
</span><span class=keyword>return </span><span class=identifier>y</span><span class=special>.</span><span class=identifier>x</span><span class=special>;
</span><span class=special>}
</span></pre></code>
<p>
The problem is that the lifetime of result X&amp; is tied to the lifetime
of y, because the f() returns a reference to a member of the y
object. This idiom is is not uncommon and perfectly acceptable in the
context of C++. However, Python users should not be able to crash the
system just by using our C++ interface. In this case deleting y will
invalidate the reference to X. We have a dangling reference.</p>
<p>
Here's what's happening:</p>
<ol><li><tt>f</tt> is called passing in a reference to <tt>y</tt> and a pointer to <tt>z</tt></li><li>A reference to <tt>y.x</tt> is returned</li><li><tt>y</tt> is deleted. <tt>x</tt> is a dangling reference</li><li><tt>x.some_method()</tt> is called</li><li><b>BOOM!</b></li></ol><p>
We could copy result into a new object:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>y</span><span class=special>, </span><span class=identifier>z</span><span class=special>).</span><span class=identifier>set</span><span class=special>(</span><span class=number>42</span><span class=special>) </span>#<span class=identifier>Result </span><span class=identifier>disappears
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>y</span><span class=special>.</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>get</span><span class=special>() </span>#<span class=identifier>No </span><span class=identifier>crash</span><span class=special>, </span><span class=identifier>but </span><span class=identifier>still </span><span class=identifier>bad
</span><span class=number>3.14
</span></pre></code>
<p>
This is not really our intent of our C++ interface. We've broken our
promise that the Python interface should reflect the C++ interface as
closely as possible.</p>
<p>
Our problems do not end there. Suppose Y is implemented as follows:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>Y
</span><span class=special>{
</span><span class=identifier>X </span><span class=identifier>x</span><span class=special>; </span><span class=identifier>Z</span><span class=special>* </span><span class=identifier>z</span><span class=special>;
</span><span class=keyword>int </span><span class=identifier>z_value</span><span class=special>() </span><span class=special>{ </span><span class=keyword>return </span><span class=identifier>z</span><span class=special>-&gt;</span><span class=identifier>value</span><span class=special>(); </span><span class=special>}
</span><span class=special>};
</span></pre></code>
<p>
Notice that the data member <tt>z</tt> is held by class Y using a raw
pointer. Now we have a potential dangling pointer problem inside Y:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>x </span><span class=special>= </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>y</span><span class=special>, </span><span class=identifier>z</span><span class=special>) </span>#<span class=identifier>y </span><span class=identifier>refers </span><span class=identifier>to </span><span class=identifier>z
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>del </span><span class=identifier>z </span>#<span class=identifier>Kill </span><span class=identifier>the </span><span class=identifier>z </span><span class=identifier>object
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>y</span><span class=special>.</span><span class=identifier>z_value</span><span class=special>() </span>#<span class=identifier>CRASH</span><span class=special>!
</span></pre></code>
<p>
For reference, here's the implementation of <tt>f</tt> again:</p>
<code><pre>
<span class=identifier>X</span><span class=special>&amp; </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>Y</span><span class=special>&amp; </span><span class=identifier>y</span><span class=special>, </span><span class=identifier>Z</span><span class=special>* </span><span class=identifier>z</span><span class=special>)
</span><span class=special>{
</span><span class=identifier>y</span><span class=special>.</span><span class=identifier>z </span><span class=special>= </span><span class=identifier>z</span><span class=special>;
</span><span class=keyword>return </span><span class=identifier>y</span><span class=special>.</span><span class=identifier>x</span><span class=special>;
</span><span class=special>}
</span></pre></code>
<p>
Here's what's happening:</p>
<ol><li><tt>f</tt> is called passing in a reference to <tt>y</tt> and a pointer to <tt>z</tt></li><li>A pointer to <tt>z</tt> is held by <tt>y</tt></li><li>A reference to <tt>y.x</tt> is returned</li><li><tt>z</tt> is deleted. <tt>y.z</tt> is a dangling pointer</li><li><tt>y.z_value()</tt> is called</li><li><tt>z-&gt;value()</tt> is called</li><li><b>BOOM!</b></li></ol><a name="call_policies"></a><h2>Call Policies</h2><p>
Call Policies may be used in situations such as the example detailed above.
In our example, <tt>return_internal_reference</tt> and <tt>with_custodian_and_ward</tt>
are our friends:</p>
<code><pre>
<span class=identifier>def</span><span class=special>(</span><span class=string>&quot;f&quot;</span><span class=special>, </span><span class=identifier>f</span><span class=special>,
</span><span class=identifier>return_internal_reference</span><span class=special>&lt;</span><span class=number>1</span><span class=special>,
</span><span class=identifier>with_custodian_and_ward</span><span class=special>&lt;</span><span class=number>1</span><span class=special>, </span><span class=number>2</span><span class=special>&gt; </span><span class=special>&gt;());
</span></pre></code>
<p>
What are the <tt>1</tt> and <tt>2</tt> parameters, you ask?</p>
<code><pre>
<span class=identifier>return_internal_reference</span><span class=special>&lt;</span><span class=number>1
</span></pre></code>
<p>
Informs Boost.Python that the first argument, in our case <tt>Y&amp; y</tt>, is the
owner of the returned reference: <tt>X&amp;</tt>. The &quot;<tt>1</tt>&quot; simply specifies the
first argument. In short: &quot;return an internal reference <tt>X&amp;</tt> owned by the
1st argument <tt>Y&amp; y</tt>&quot;.</p>
<code><pre>
<span class=identifier>with_custodian_and_ward</span><span class=special>&lt;</span><span class=number>1</span><span class=special>, </span><span class=number>2</span><span class=special>&gt;
</span></pre></code>
<p>
Informs Boost.Python that the lifetime of the argument indicated by ward
(i.e. the 2nd argument: <tt>Z* z</tt>) is dependent on the lifetime of the
argument indicated by custodian (i.e. the 1st argument: <tt>Y&amp; y</tt>).</p>
<p>
It is also important to note that we have defined two policies above. Two
or more policies can be composed by chaining. Here's the general syntax:</p>
<code><pre>
<span class=identifier>policy1</span><span class=special>&lt;</span><span class=identifier>args</span><span class=special>...,
</span><span class=identifier>policy2</span><span class=special>&lt;</span><span class=identifier>args</span><span class=special>...,
</span><span class=identifier>policy3</span><span class=special>&lt;</span><span class=identifier>args</span><span class=special>...&gt; </span><span class=special>&gt; </span><span class=special>&gt;
</span></pre></code>
<p>
Here is the list of predefined call policies. A complete reference detailing
these can be found <a href="../../v2/reference.html#models_of_call_policies">
here</a>.</p>
<ul><li><b>with_custodian_and_ward</b><br> Ties lifetimes of the arguments</li><li><b>with_custodian_and_ward_postcall</b><br> Ties lifetimes of the arguments and results</li><li><b>return_internal_reference</b><br> Ties lifetime of one argument to that of result</li><li><b>return_value_policy&lt;T&gt; with T one of:</b><br></li><li><b>reference_existing_object</b><br>naïve (dangerous) approach</li><li><b>copy_const_reference</b><br>Boost.Python v1 approach</li><li><b>copy_non_const_reference</b><br></li><li><b>manage_new_object</b><br> Adopt a pointer and hold the instance</li></ul><table width="80%" border="0" align="center">
<tr>
<td class="note_box">
<img src="theme/smiley.gif"></img> <b>Remember the Zen, Luke:</b><br><br>
&quot;Explicit is better than implicit&quot;<br>
&quot;In the face of ambiguity, refuse the temptation to guess&quot;<br> </td>
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<br>
<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
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is provided &quot;as is&quot; without express or implied warranty, and with
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<p>
Data members may also be exposed to Python so that they can be
accessed as attributes of the corresponding Python class. Each data
member that we wish to be exposed may be regarded as <b>read-only</b> or
<b>read-write</b>. Consider this class <tt>Var</tt>:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>Var
</span><span class=special>{
</span><span class=identifier>Var</span><span class=special>(</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>name</span><span class=special>) </span><span class=special>: </span><span class=identifier>name</span><span class=special>(</span><span class=identifier>name</span><span class=special>), </span><span class=identifier>value</span><span class=special>() </span><span class=special>{}
</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=keyword>const </span><span class=identifier>name</span><span class=special>;
</span><span class=keyword>float </span><span class=identifier>value</span><span class=special>;
</span><span class=special>};
</span></pre></code>
<p>
Our C++ <tt>Var</tt> class and its data members can be exposed to Python:</p>
<code><pre>
<span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>Var</span><span class=special>&gt;(</span><span class=string>&quot;Var&quot;</span><span class=special>, </span><span class=identifier>init</span><span class=special>&lt;</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>&gt;())
</span><span class=special>.</span><span class=identifier>def_readonly</span><span class=special>(</span><span class=string>&quot;name&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>Var</span><span class=special>::</span><span class=identifier>name</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def_readwrite</span><span class=special>(</span><span class=string>&quot;value&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>Var</span><span class=special>::</span><span class=identifier>value</span><span class=special>);
</span></pre></code>
<p>
Then, in Python:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>x </span><span class=special>= </span><span class=identifier>Var</span><span class=special>(</span><span class=literal>'pi'</span><span class=special>)
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>value </span><span class=special>= </span><span class=number>3.14
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>print </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>name</span><span class=special>, </span><span class=literal>'is around'</span><span class=special>, </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>value
</span><span class=identifier>pi </span><span class=identifier>is </span><span class=identifier>around </span><span class=number>3.14
</span></pre></code>
<p>
Note that <tt>name</tt> is exposed as <b>read-only</b> while <tt>value</tt> is exposed
as <b>read-write</b>.</p>
<code><pre>
&gt;&gt;&gt; x.name = 'e' # can't change name
Traceback (most recent call last):
File &quot;&lt;stdin&gt;&quot;, line 1, in ?
AttributeError: can't set attribute
</pre></code><table border="0">
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<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
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<a name="python_operators"></a><h2>Python Operators</h2><p>
C is well known for the abundance of operators. C++ extends this to the
extremes by allowing operator overloading. Boost.Python takes advantage of
this and makes it easy to wrap C++ operator-powered classes.</p>
<p>
Consider a file position class <tt>FilePos</tt> and a set of operators that take
on FilePos instances:</p>
<code><pre>
<span class=keyword>class </span><span class=identifier>FilePos </span><span class=special>{ </span><span class=comment>/*...*/ </span><span class=special>};
</span><span class=identifier>FilePos </span><span class=keyword>operator</span><span class=special>+(</span><span class=identifier>FilePos</span><span class=special>, </span><span class=keyword>int</span><span class=special>);
</span><span class=identifier>FilePos </span><span class=keyword>operator</span><span class=special>+(</span><span class=keyword>int</span><span class=special>, </span><span class=identifier>FilePos</span><span class=special>);
</span><span class=keyword>int </span><span class=keyword>operator</span><span class=special>-(</span><span class=identifier>FilePos</span><span class=special>, </span><span class=identifier>FilePos</span><span class=special>);
</span><span class=identifier>FilePos </span><span class=keyword>operator</span><span class=special>-(</span><span class=identifier>FilePos</span><span class=special>, </span><span class=keyword>int</span><span class=special>);
</span><span class=identifier>FilePos</span><span class=special>&amp; </span><span class=keyword>operator</span><span class=special>+=(</span><span class=identifier>FilePos</span><span class=special>&amp;, </span><span class=keyword>int</span><span class=special>);
</span><span class=identifier>FilePos</span><span class=special>&amp; </span><span class=keyword>operator</span><span class=special>-=(</span><span class=identifier>FilePos</span><span class=special>&amp;, </span><span class=keyword>int</span><span class=special>);
</span><span class=keyword>bool </span><span class=keyword>operator</span><span class=special>&lt;(</span><span class=identifier>FilePos</span><span class=special>, </span><span class=identifier>FilePos</span><span class=special>);
</span></pre></code>
<p>
The class and the various operators can be mapped to Python rather easily
and intuitively:</p>
<code><pre>
<span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>FilePos</span><span class=special>&gt;(</span><span class=string>&quot;FilePos&quot;</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>self </span><span class=special>+ </span><span class=keyword>int</span><span class=special>()) </span><span class=comment>// __add__
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=keyword>int</span><span class=special>() </span><span class=special>+ </span><span class=identifier>self</span><span class=special>) </span><span class=comment>// __radd__
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>self </span><span class=special>- </span><span class=identifier>self</span><span class=special>) </span><span class=comment>// __sub__
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>self </span><span class=special>- </span><span class=keyword>int</span><span class=special>()) </span><span class=comment>// __rsub__
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>self </span><span class=special>+= </span><span class=keyword>int</span><span class=special>()) </span><span class=comment>// __iadd__
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>self </span><span class=special>-= </span><span class=identifier>other</span><span class=special>&lt;</span><span class=keyword>int</span><span class=special>&gt;())
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>self </span><span class=special>&lt; </span><span class=identifier>self</span><span class=special>); </span><span class=comment>// __lt__
</span></pre></code>
<p>
The code snippet above is very clear and needs almost no explanation at
all. It is virtually the same as the operators' signatures. Just take
note that <tt>self</tt> refers to FilePos object. Also, not every class <tt>T</tt> that
you might need to interact with in an operator expression is (cheaply)
default-constructible. You can use <tt>other&lt;T&gt;()</tt> in place of an actual
<tt>T</tt> instance when writing &quot;self expressions&quot;.</p>
<a name="special_methods"></a><h2>Special Methods</h2><p>
Python has a few more <i>Special Methods</i>. Boost.Python supports all of the
standard special method names supported by real Python class instances. A
similar set of intuitive interfaces can also be used to wrap C++ functions
that correspond to these Python <i>special functions</i>. Example:</p>
<code><pre>
<span class=keyword>class </span><span class=identifier>Rational
</span><span class=special>{ </span><span class=keyword>operator </span><span class=keyword>double</span><span class=special>() </span><span class=keyword>const</span><span class=special>; </span><span class=special>};
</span><span class=identifier>Rational </span><span class=identifier>pow</span><span class=special>(</span><span class=identifier>Rational</span><span class=special>, </span><span class=identifier>Rational</span><span class=special>);
</span><span class=identifier>Rational </span><span class=identifier>abs</span><span class=special>(</span><span class=identifier>Rational</span><span class=special>);
</span><span class=identifier>ostream</span><span class=special>&amp; </span><span class=keyword>operator</span><span class=special>&lt;&lt;(</span><span class=identifier>ostream</span><span class=special>&amp;,</span><span class=identifier>Rational</span><span class=special>);
</span><span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>Rational</span><span class=special>&gt;()
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>float_</span><span class=special>(</span><span class=identifier>self</span><span class=special>)) </span><span class=comment>// __float__
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>pow</span><span class=special>(</span><span class=identifier>self</span><span class=special>, </span><span class=identifier>other</span><span class=special>&lt;</span><span class=identifier>Rational</span><span class=special>&gt;)) </span><span class=comment>// __pow__
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>abs</span><span class=special>(</span><span class=identifier>self</span><span class=special>)) </span><span class=comment>// __abs__
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>str</span><span class=special>(</span><span class=identifier>self</span><span class=special>)) </span><span class=comment>// __str__
</span><span class=special>;
</span></pre></code>
<p>
Need we say more?</p>
<table width="80%" border="0" align="center">
<tr>
<td class="note_box">
<img src="theme/lens.gif"></img> What is the business of <tt>operator&lt;&lt;</tt> <tt>.def(str(self))</tt>?
Well, the method <tt>str</tt> requires the <tt>operator&lt;&lt;</tt> to do its work (i.e.
<tt>operator&lt;&lt;</tt> is used by the method defined by def(str(self)). </td>
</tr>
</table>
<table border="0">
<tr>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
<td width="30"><a href="class_virtual_functions.html"><img src="theme/l_arr.gif" border="0"></a></td>
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</table>
<br>
<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
is granted provided this copyright notice appears in all copies. This document
is provided &quot;as is&quot; without express or implied warranty, and with
no claim as to its suitability for any purpose. </font> </p>
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@@ -1,81 +0,0 @@
<html>
<head>
<!-- Generated by the Spirit (http://spirit.sf.net) QuickDoc -->
<title>Class Properties</title>
<link rel="stylesheet" href="theme/style.css" type="text/css">
<link rel="prev" href="class_data_members.html">
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</head>
<body>
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<td><img src="theme/c%2B%2Bboost.gif">
</td>
<td width="85%">
<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Class Properties</b></font>
</td>
</tr>
</table>
<br>
<table border="0">
<tr>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
<td width="30"><a href="class_data_members.html"><img src="theme/l_arr.gif" border="0"></a></td>
<td width="20"><a href="inheritance.html"><img src="theme/r_arr.gif" border="0"></a></td>
</tr>
</table>
<p>
In C++, classes with public data members are usually frowned
upon. Well designed classes that take advantage of encapsulation hide
the class' data members. The only way to access the class' data is
through access (getter/setter) functions. Access functions expose class
properties. Here's an example:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>Num
</span><span class=special>{
</span><span class=identifier>Num</span><span class=special>();
</span><span class=keyword>float </span><span class=identifier>get</span><span class=special>() </span><span class=keyword>const</span><span class=special>;
</span><span class=keyword>void </span><span class=identifier>set</span><span class=special>(</span><span class=keyword>float </span><span class=identifier>value</span><span class=special>);
</span><span class=special>...
</span><span class=special>};
</span></pre></code>
<p>
However, in Python attribute access is fine; it doesn't neccessarily break
encapsulation to let users handle attributes directly, because the
attributes can just be a different syntax for a method call. Wrapping our
<tt>Num</tt> class using Boost.Python:</p>
<code><pre>
<span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>Num</span><span class=special>&gt;(</span><span class=string>&quot;Num&quot;</span><span class=special>)
</span><span class=special>.</span><span class=identifier>add_property</span><span class=special>(</span><span class=string>&quot;rovalue&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>Var</span><span class=special>::</span><span class=identifier>get</span><span class=special>)
</span><span class=special>.</span><span class=identifier>add_property</span><span class=special>(</span><span class=string>&quot;value&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>Var</span><span class=special>::</span><span class=identifier>get</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>Var</span><span class=special>::</span><span class=identifier>set</span><span class=special>);
</span></pre></code>
<p>
And at last, in Python:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>x </span><span class=special>= </span><span class=identifier>Num</span><span class=special>()
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>value </span><span class=special>= </span><span class=number>3.14
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>value</span><span class=special>, </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>rovalue
</span><span class=special>(</span><span class=number>3.14</span><span class=special>, </span><span class=number>3.14</span><span class=special>)
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>rovalue </span><span class=special>= </span><span class=number>2.17 </span>#<span class=identifier>error</span><span class=special>!
</span></pre></code>
<p>
Take note that the class property <tt>rovalue</tt> is exposed as <b>read-only</b>
since the <tt>rovalue</tt> setter member function is not passed in:</p>
<code><pre>
<span class=special>.</span><span class=identifier>add_property</span><span class=special>(</span><span class=string>&quot;rovalue&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>Var</span><span class=special>::</span><span class=identifier>get</span><span class=special>)
</span></pre></code>
<table border="0">
<tr>
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</tr>
</table>
<br>
<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
is granted provided this copyright notice appears in all copies. This document
is provided &quot;as is&quot; without express or implied warranty, and with
no claim as to its suitability for any purpose. </font> </p>
</body>
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@@ -1,227 +0,0 @@
<html>
<head>
<!-- Generated by the Spirit (http://spirit.sf.net) QuickDoc -->
<title>Class Virtual Functions</title>
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</td>
<td width="85%">
<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Class Virtual Functions</b></font>
</td>
</tr>
</table>
<br>
<table border="0">
<tr>
<td width="30"><a href="../index.html"><img src="theme/u_arr.gif" border="0"></a></td>
<td width="30"><a href="inheritance.html"><img src="theme/l_arr.gif" border="0"></a></td>
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</table>
<p>
In this section, we shall learn how to make functions behave
polymorphically through virtual functions. Continuing our example, let us
add a virtual function to our <tt>Base</tt> class:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>Base
</span><span class=special>{
</span><span class=keyword>virtual </span><span class=keyword>int </span><span class=identifier>f</span><span class=special>() </span><span class=special>= </span><span class=number>0</span><span class=special>;
</span><span class=special>};
</span></pre></code>
<p>
Since <tt>f</tt> is a pure virtual function, <tt>Base</tt> is now an abstract
class. Given an instance of our class, the free function <tt>call_f</tt>
calls some implementation of this virtual function in a concrete
derived class:</p>
<code><pre>
<span class=keyword>int </span><span class=identifier>call_f</span><span class=special>(</span><span class=identifier>Base</span><span class=special>&amp; </span><span class=identifier>b</span><span class=special>) </span><span class=special>{ </span><span class=keyword>return </span><span class=identifier>b</span><span class=special>.</span><span class=identifier>f</span><span class=special>(); </span><span class=special>}
</span></pre></code>
<p>
To allow this function to be implemented in a Python derived class, we
need to create a class wrapper:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>BaseWrap </span><span class=special>: </span><span class=identifier>Base
</span><span class=special>{
</span><span class=identifier>BaseWrap</span><span class=special>(</span><span class=identifier>PyObject</span><span class=special>* </span><span class=identifier>self_</span><span class=special>)
</span><span class=special>: </span><span class=identifier>self</span><span class=special>(</span><span class=identifier>self_</span><span class=special>) </span><span class=special>{}
</span><span class=keyword>int </span><span class=identifier>f</span><span class=special>() </span><span class=special>{ </span><span class=keyword>return </span><span class=identifier>call_method</span><span class=special>&lt;</span><span class=keyword>int</span><span class=special>&gt;(</span><span class=identifier>self</span><span class=special>, </span><span class=string>&quot;f&quot;</span><span class=special>); </span><span class=special>}
</span><span class=identifier>PyObject</span><span class=special>* </span><span class=identifier>self</span><span class=special>;
</span><span class=special>};
</span></pre></code>
<table width="80%" border="0" align="center">
<tr>
<td class="note_box">
<img src="theme/lens.gif"></img> <b>member function and methods</b><br><br> Python, like
many object oriented languages uses the term <b>methods</b>. Methods
correspond roughly to C++'s <b>member functions</b> </td>
</tr>
</table>
<p>
Our class wrapper <tt>BaseWrap</tt> is derived from <tt>Base</tt>. Its overridden
virtual member function <tt>f</tt> in effect calls the corresponding method
of the Python object <tt>self</tt>, which is a pointer back to the Python
<tt>Base</tt> object holding our <tt>BaseWrap</tt> instance.</p>
<table width="80%" border="0" align="center">
<tr>
<td class="note_box">
<img src="theme/note.gif"></img> <b>Why do we need BaseWrap?</b><br><br>
<i>You may ask</i>, &quot;Why do we need the <tt>BaseWrap</tt> derived class? This could
have been designed so that everything gets done right inside of
Base.&quot;<br><br>
One of the goals of Boost.Python is to be minimally intrusive on an
existing C++ design. In principle, it should be possible to expose the
interface for a 3rd party library without changing it. To unintrusively
hook into the virtual functions so that a Python override may be called, we
must use a derived class.<br><br>
Note however that you don't need to do this to get methods overridden
in Python to behave virtually when called <i>from</i> <b>Python</b>. The only
time you need to do the <tt>BaseWrap</tt> dance is when you have a virtual
function that's going to be overridden in Python and called
polymorphically <i>from</i> <b>C++</b>. </td>
</tr>
</table>
<p>
Wrapping <tt>Base</tt> and the free function <tt>call_f</tt>:</p>
<code><pre>
<span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>Base</span><span class=special>, </span><span class=identifier>BaseWrap</span><span class=special>, </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>noncopyable</span><span class=special>&gt;(</span><span class=string>&quot;Base&quot;</span><span class=special>, </span><span class=identifier>no_init</span><span class=special>)
</span><span class=special>;
</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;call_f&quot;</span><span class=special>, </span><span class=identifier>call_f</span><span class=special>);
</span></pre></code>
<p>
Notice that we parameterized the <tt>class_</tt> template with <tt>BaseWrap</tt> as the
second parameter. What is <tt>noncopyable</tt>? Without it, the library will try
to create code for converting Base return values of wrapped functions to
Python. To do that, it needs Base's copy constructor... which isn't
available, since Base is an abstract class.</p>
<p>
In Python, let us try to instantiate our <tt>Base</tt> class:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>base </span><span class=special>= </span><span class=identifier>Base</span><span class=special>()
</span><span class=identifier>AttributeError</span><span class=special>: </span><span class=special>...
</span></pre></code>
<p>
Why is it an error? <tt>Base</tt> is an abstract class. As such it is advisable
to define the Python wrapper with <tt>no_init</tt> as we have done above. Doing
so will disallow abstract base classes such as <tt>Base</tt> to be instantiated.</p>
<a name="deriving_a_python_class"></a><h2>Deriving a Python class</h2><p>
Now, at last, we can even derive from our base class <tt>Base</tt> in Python:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=keyword>class </span><span class=identifier>Derived</span><span class=special>(</span><span class=identifier>Base</span><span class=special>):
</span><span class=special>... </span><span class=identifier>def </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>self</span><span class=special>):
</span><span class=special>... </span><span class=keyword>return </span><span class=number>42
</span><span class=special>...
</span></pre></code>
<p>
Cool eh? A Python class deriving from a C++ class!</p>
<p>
Let's now make an instance of our Python class <tt>Derived</tt>:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>derived </span><span class=special>= </span><span class=identifier>Derived</span><span class=special>()
</span></pre></code>
<p>
Calling <tt>derived.f()</tt>:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>derived</span><span class=special>.</span><span class=identifier>f</span><span class=special>()
</span><span class=number>42
</span></pre></code>
<p>
Will yield the expected result. Finally, calling calling the free function
<tt>call_f</tt> with <tt>derived</tt> as argument:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>call_f</span><span class=special>(</span><span class=identifier>derived</span><span class=special>)
</span><span class=number>42
</span></pre></code>
<p>
Will also yield the expected result.</p>
<p>
Here's what's happening:</p>
<ol><li><tt>call_f(derived)</tt> is called in Python</li><li>This corresponds to <tt>def(&quot;call_f&quot;, call_f);</tt>. Boost.Python dispatches this call.</li><li><tt>int call_f(Base&amp; b) { return b.f(); }</tt> accepts the call.</li><li>The overridden virtual function <tt>f</tt> of <tt>BaseWrap</tt> is called.</li><li><tt>call_method&lt;int&gt;(self, &quot;f&quot;);</tt> dispatches the call back to Python.</li><li><tt>def f(self): return 42</tt> is finally called.</li></ol><p>
Rewind back to our <tt>Base</tt> class, if its member function <tt>f</tt> was not
declared as pure virtual:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>Base
</span><span class=special>{
</span><span class=keyword>virtual </span><span class=keyword>int </span><span class=identifier>f</span><span class=special>() </span><span class=special>{ </span><span class=keyword>return </span><span class=number>0</span><span class=special>; </span><span class=special>}
</span><span class=special>};
</span></pre></code>
<p>
And instead is implemented to return <tt>0</tt>, as shown above.</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>BaseWrap </span><span class=special>: </span><span class=identifier>Base
</span><span class=special>{
</span><span class=identifier>BaseWrap</span><span class=special>(</span><span class=identifier>PyObject</span><span class=special>* </span><span class=identifier>self_</span><span class=special>)
</span><span class=special>: </span><span class=identifier>self</span><span class=special>(</span><span class=identifier>self_</span><span class=special>) </span><span class=special>{}
</span><span class=keyword>int </span><span class=identifier>f</span><span class=special>() </span><span class=special>{ </span><span class=keyword>return </span><span class=identifier>call_method</span><span class=special>&lt;</span><span class=keyword>int</span><span class=special>&gt;(</span><span class=identifier>self</span><span class=special>, </span><span class=string>&quot;f&quot;</span><span class=special>); </span><span class=special>}
</span><span class=keyword>static </span><span class=keyword>int </span><span class=identifier>default_f</span><span class=special>(</span><span class=identifier>Base</span><span class=special>* </span><span class=identifier>b</span><span class=special>) </span><span class=special>{ </span><span class=keyword>return </span><span class=identifier>b</span><span class=special>-&gt;</span><span class=identifier>Base</span><span class=special>::</span><span class=identifier>f</span><span class=special>(); </span><span class=special>} </span><span class=comment>// &lt;&lt;=== added
</span><span class=identifier>PyObject</span><span class=special>* </span><span class=identifier>self</span><span class=special>;
</span><span class=special>};
</span></pre></code>
<p>
then, our Boost.Python wrapper:</p>
<code><pre>
<span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>Base</span><span class=special>, </span><span class=identifier>BaseWrap</span><span class=special>&gt;(</span><span class=string>&quot;Base&quot;</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;f&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>BaseWrap</span><span class=special>::</span><span class=identifier>default_f</span><span class=special>)
</span><span class=special>;
</span></pre></code>
<p>
Note that we are allowing <tt>Base</tt> objects to be instantiated this time,
unlike before where we specifically defined the <tt>class_&lt;Base&gt;</tt> with
<tt>no_init</tt>.</p>
<p>
In Python, the results would be as expected:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>base </span><span class=special>= </span><span class=identifier>Base</span><span class=special>()
</span><span class=special>&gt;&gt;&gt; </span><span class=keyword>class </span><span class=identifier>Derived</span><span class=special>(</span><span class=identifier>Base</span><span class=special>):
</span><span class=special>... </span><span class=identifier>def </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>self</span><span class=special>):
</span><span class=special>... </span><span class=keyword>return </span><span class=number>42
</span><span class=special>...
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>derived </span><span class=special>= </span><span class=identifier>Derived</span><span class=special>()
</span></pre></code>
<p>
Calling <tt>base.f()</tt>:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>base</span><span class=special>.</span><span class=identifier>f</span><span class=special>()
</span><span class=number>0
</span></pre></code>
<p>
Calling <tt>derived.f()</tt>:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>derived</span><span class=special>.</span><span class=identifier>f</span><span class=special>()
</span><span class=number>42
</span></pre></code>
<p>
Calling <tt>call_f</tt>, passing in a <tt>base</tt> object:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>call_f</span><span class=special>(</span><span class=identifier>base</span><span class=special>)
</span><span class=number>0
</span></pre></code>
<p>
Calling <tt>call_f</tt>, passing in a <tt>derived</tt> object:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>call_f</span><span class=special>(</span><span class=identifier>derived</span><span class=special>)
</span><span class=number>42
</span></pre></code>
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<p>
Our previous example didn't have any explicit constructors.
Since <tt>World</tt> is declared as a plain struct, it has an implicit default
constructor. Boost.Python exposes the default constructor by default,
which is why we were able to write</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>planet </span><span class=special>= </span><span class=identifier>hello</span><span class=special>.</span><span class=identifier>World</span><span class=special>()
</span></pre></code>
<p>
We may wish to wrap a class with a non-default constructor. Let us
build on our previous example:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>World
</span><span class=special>{
</span><span class=identifier>World</span><span class=special>(</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>msg</span><span class=special>): </span><span class=identifier>msg</span><span class=special>(</span><span class=identifier>msg</span><span class=special>) </span><span class=special>{} </span><span class=comment>// added constructor
</span><span class=keyword>void </span><span class=identifier>set</span><span class=special>(</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>msg</span><span class=special>) </span><span class=special>{ </span><span class=keyword>this</span><span class=special>-&gt;</span><span class=identifier>msg </span><span class=special>= </span><span class=identifier>msg</span><span class=special>; </span><span class=special>}
</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>greet</span><span class=special>() </span><span class=special>{ </span><span class=keyword>return </span><span class=identifier>msg</span><span class=special>; </span><span class=special>}
</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>msg</span><span class=special>;
</span><span class=special>};
</span></pre></code>
<p>
This time <tt>World</tt> has no default constructor; our previous
wrapping code would fail to compile when the library tried to expose
it. We have to tell <tt>class_&lt;World&gt;</tt> about the constructor we want to
expose instead.</p>
<code><pre>
<span class=preprocessor>#include </span><span class=special>&lt;</span><span class=identifier>boost</span><span class=special>/</span><span class=identifier>python</span><span class=special>.</span><span class=identifier>hpp</span><span class=special>&gt;
</span><span class=keyword>using </span><span class=keyword>namespace </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>python</span><span class=special>;
</span><span class=identifier>BOOST_PYTHON_MODULE</span><span class=special>(</span><span class=identifier>hello</span><span class=special>)
</span><span class=special>{
</span><span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>World</span><span class=special>&gt;(</span><span class=string>&quot;World&quot;</span><span class=special>, </span><span class=identifier>init</span><span class=special>&lt;</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>&gt;())
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;greet&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>World</span><span class=special>::</span><span class=identifier>greet</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;set&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>World</span><span class=special>::</span><span class=identifier>set</span><span class=special>)
</span><span class=special>;
</span><span class=special>}
</span></pre></code>
<p>
<tt>init&lt;std::string&gt;()</tt> exposes the constructor taking in a
<tt>std::string</tt> (in Python, constructors are spelled
&quot;<tt>&quot;__init__&quot;</tt>&quot;).</p>
<p>
We can expose additional constructors by passing more <tt>init&lt;...&gt;</tt>s to
the <tt>def()</tt> member function. Say for example we have another World
constructor taking in two doubles:</p>
<code><pre>
<span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>World</span><span class=special>&gt;(</span><span class=string>&quot;World&quot;</span><span class=special>, </span><span class=identifier>init</span><span class=special>&lt;</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>&gt;())
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>init</span><span class=special>&lt;</span><span class=keyword>double</span><span class=special>, </span><span class=keyword>double</span><span class=special>&gt;())
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;greet&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>World</span><span class=special>::</span><span class=identifier>greet</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;set&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>World</span><span class=special>::</span><span class=identifier>set</span><span class=special>)
</span><span class=special>;
</span></pre></code>
<p>
On the other hand, if we do not wish to expose any constructors at
all, we may use <tt>no_init</tt> instead:</p>
<code><pre>
<span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>Abstract</span><span class=special>&gt;(</span><span class=string>&quot;Abstract&quot;</span><span class=special>, </span><span class=identifier>no_init</span><span class=special>)
</span></pre></code>
<p>
This actually adds an <tt>__init__</tt> method which always raises a
Python RuntimeError exception.</p>
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<p>
Boost.Python wraps (member) function pointers. Unfortunately, C++ function
pointers carry no default argument info. Take a function <tt>f</tt> with default
arguments:</p>
<code><pre>
<span class=keyword>int </span><span class=identifier>f</span><span class=special>(</span><span class=keyword>int</span><span class=special>, </span><span class=keyword>double </span><span class=special>= </span><span class=number>3.14</span><span class=special>, </span><span class=keyword>char </span><span class=keyword>const</span><span class=special>* </span><span class=special>= </span><span class=string>&quot;hello&quot;</span><span class=special>);
</span></pre></code>
<p>
But the type of a pointer to the function <tt>f</tt> has no information
about its default arguments:</p>
<code><pre>
<span class=keyword>int</span><span class=special>(*</span><span class=identifier>g</span><span class=special>)(</span><span class=keyword>int</span><span class=special>,</span><span class=keyword>double</span><span class=special>,</span><span class=keyword>char </span><span class=keyword>const</span><span class=special>*) </span><span class=special>= </span><span class=identifier>f</span><span class=special>; </span><span class=comment>// defaults lost!
</span></pre></code>
<p>
When we pass this function pointer to the <tt>def</tt> function, there is no way
to retrieve the default arguments:</p>
<code><pre>
<span class=identifier>def</span><span class=special>(</span><span class=string>&quot;f&quot;</span><span class=special>, </span><span class=identifier>f</span><span class=special>); </span><span class=comment>// defaults lost!
</span></pre></code>
<p>
Because of this, when wrapping C++ code in earlier versions of
Boost.Python, we had to resort to writing thin wrappers:</p>
<code><pre>
<span class=comment>// write &quot;thin wrappers&quot;
</span><span class=keyword>int </span><span class=identifier>f1</span><span class=special>(</span><span class=keyword>int </span><span class=identifier>x</span><span class=special>) </span><span class=special>{ </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>x</span><span class=special>); </span><span class=special>}
</span><span class=keyword>int </span><span class=identifier>f2</span><span class=special>(</span><span class=keyword>int </span><span class=identifier>x</span><span class=special>, </span><span class=keyword>double </span><span class=identifier>y</span><span class=special>) </span><span class=special>{ </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>x</span><span class=special>,</span><span class=identifier>y</span><span class=special>); </span><span class=special>}
</span><span class=comment>/*...*/
// in module init
</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;f&quot;</span><span class=special>, </span><span class=identifier>f</span><span class=special>); </span><span class=comment>// all arguments
</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;f&quot;</span><span class=special>, </span><span class=identifier>f2</span><span class=special>); </span><span class=comment>// two arguments
</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;f&quot;</span><span class=special>, </span><span class=identifier>f1</span><span class=special>); </span><span class=comment>// one argument
</span></pre></code>
<p>
When you want to wrap functions (or member functions) that either:</p>
<ul><li>have default arguments, or</li><li>are overloaded with a common sequence of initial arguments</li></ul><p>
Boost.Python now has a way to make it easier.</p>
<p>
For instance, given a function:</p>
<code><pre>
<span class=keyword>int </span><span class=identifier>foo</span><span class=special>(</span><span class=keyword>int </span><span class=identifier>a</span><span class=special>, </span><span class=keyword>char </span><span class=identifier>b </span><span class=special>= </span><span class=number>1</span><span class=special>, </span><span class=keyword>unsigned </span><span class=identifier>c </span><span class=special>= </span><span class=number>2</span><span class=special>, </span><span class=keyword>double </span><span class=identifier>d </span><span class=special>= </span><span class=number>3</span><span class=special>);
</span></pre></code>
<p>
The macro invocation:</p>
<code><pre>
<span class=identifier>BOOST_PYTHON_FUNCTION_OVERLOADS</span><span class=special>(</span><span class=identifier>foo_overloads</span><span class=special>, </span><span class=identifier>foo</span><span class=special>, </span><span class=number>1</span><span class=special>, </span><span class=number>4</span><span class=special>)
</span></pre></code>
<p>
Will automatically create the thin wrappers for us. This macro will create
a class <tt>foo_overloads</tt> that can be passed on to <tt>def(...)</tt>. The third
and fourth macro argument are the minimum arguments and maximum arguments,
respectively. In our <tt>foo</tt> function the minimum number of arguments is 1
and the maximum number of arguments is 4. The <tt>def(...)</tt> function will
automatically add all the foo variants for us:</p>
<code><pre>
<span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;foo&quot;</span><span class=special>, </span><span class=identifier>foo</span><span class=special>, </span><span class=identifier>foo_overloads</span><span class=special>());
</span></pre></code>
<p>
A similar facility is provided for class constructors, again, with
default arguments or a sequence of overloads. Remember init&lt;...&gt;? For example,
given a class X with a constructor:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>X
</span><span class=special>{
</span><span class=identifier>X</span><span class=special>(</span><span class=keyword>int </span><span class=identifier>a</span><span class=special>, </span><span class=keyword>char </span><span class=identifier>b </span><span class=special>= </span><span class=literal>'D'</span><span class=special>, </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>c </span><span class=special>= </span><span class=string>&quot;constructor&quot;</span><span class=special>, </span><span class=keyword>double </span><span class=identifier>d </span><span class=special>= </span><span class=number>0.0</span><span class=special>);
</span><span class=comment>/*...*/
</span><span class=special>}
</span></pre></code>
<p>
You can easily add this constructor to Boost.Python in one shot:</p>
<code><pre>
<span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=identifier>init</span><span class=special>&lt;</span><span class=keyword>int</span><span class=special>, </span><span class=identifier>optional</span><span class=special>&lt;</span><span class=keyword>char</span><span class=special>, </span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string</span><span class=special>, </span><span class=keyword>double</span><span class=special>&gt; </span><span class=special>&gt;())
</span></pre></code>
<p>
Notice the use of <tt>init&lt;...&gt;</tt> and <tt>optional&lt;...&gt;</tt> to signify the default
(optional arguments).</p>
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<p>
Boost.Python comes with a set of derived <tt>object</tt> types corresponding to
that of Python's:</p>
<ul><li>list</li><li>dict</li><li>tuple</li><li>str</li><li>long_</li><li>enum</li></ul><p>
These derived <tt>object</tt> types act like real Python types. For instance:</p>
<code><pre>
<span class=identifier>str</span><span class=special>(</span><span class=number>1</span><span class=special>) </span><span class=special>==&gt; </span><span class=string>&quot;1&quot;
</span></pre></code>
<p>
Wherever appropriate, a particular derived <tt>object</tt> has corresponding
Python type's methods. For instance, <tt>dict</tt> has a <tt>keys()</tt> method:</p>
<code><pre>
<span class=identifier>d</span><span class=special>.</span><span class=identifier>keys</span><span class=special>()
</span></pre></code>
<p>
<tt>make_tuple</tt> is provided for declaring <i>tuple literals</i>. Example:</p>
<code><pre>
<span class=identifier>make_tuple</span><span class=special>(</span><span class=number>123</span><span class=special>, </span><span class=literal>'D'</span><span class=special>, </span><span class=string>&quot;Hello, World&quot;</span><span class=special>, </span><span class=number>0.0</span><span class=special>);
</span></pre></code>
<p>
In C++, when Boost.Python <tt>object</tt>s are used as arguments to functions,
subtype matching is required. For example, when a function <tt>f</tt>, as
declared below, is wrapped, it will only accept instances of Python's
<tt>str</tt> type and subtypes.</p>
<code><pre>
<span class=keyword>void </span><span class=identifier>f</span><span class=special>(</span><span class=identifier>str </span><span class=identifier>name</span><span class=special>)
</span><span class=special>{
</span><span class=identifier>object </span><span class=identifier>n2 </span><span class=special>= </span><span class=identifier>name</span><span class=special>.</span><span class=identifier>attr</span><span class=special>(</span><span class=string>&quot;upper&quot;</span><span class=special>)(); </span><span class=comment>// NAME = name.upper()
</span><span class=identifier>str </span><span class=identifier>NAME </span><span class=special>= </span><span class=identifier>name</span><span class=special>.</span><span class=identifier>upper</span><span class=special>(); </span><span class=comment>// better
</span><span class=identifier>object </span><span class=identifier>msg </span><span class=special>= </span><span class=string>&quot;%s is bigger than %s&quot; </span><span class=special>% </span><span class=identifier>make_tuple</span><span class=special>(</span><span class=identifier>NAME</span><span class=special>,</span><span class=identifier>name</span><span class=special>);
</span><span class=special>}
</span></pre></code>
<p>
In finer detail:</p>
<code><pre>
<span class=identifier>str </span><span class=identifier>NAME </span><span class=special>= </span><span class=identifier>name</span><span class=special>.</span><span class=identifier>upper</span><span class=special>();
</span></pre></code>
<p>
Illustrates that we provide versions of the str type's methods as C++
member functions.</p>
<code><pre>
<span class=identifier>object </span><span class=identifier>msg </span><span class=special>= </span><span class=string>&quot;%s is bigger than %s&quot; </span><span class=special>% </span><span class=identifier>make_tuple</span><span class=special>(</span><span class=identifier>NAME</span><span class=special>,</span><span class=identifier>name</span><span class=special>);
</span></pre></code>
<p>
Demonstrates that you can write the C++ equivalent of <tt>&quot;format&quot; % x,y,z</tt>
in Python, which is useful since there's no easy way to do that in std C++.</p>
<p>
<img src="theme/alert.gif"></img> <b>Beware</b> the common pitfall of forgetting that the constructors
of most of Python's mutable types make copies, just as in Python.</p>
<p>
Python:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>d </span><span class=special>= </span><span class=identifier>dict</span><span class=special>(</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>__dict__</span><span class=special>) </span>#<span class=identifier>copies </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>__dict__
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>d</span><span class=special>[</span><span class=literal>'whatever'</span><span class=special>] </span>#<span class=identifier>modifies </span><span class=identifier>the </span><span class=identifier>copy
</span></pre></code>
<p>
C++:</p>
<code><pre>
<span class=identifier>dict </span><span class=identifier>d</span><span class=special>(</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>attr</span><span class=special>(</span><span class=string>&quot;__dict__&quot;</span><span class=special>)); </span>#<span class=identifier>copies </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>__dict__
</span><span class=identifier>d</span><span class=special>[</span><span class=literal>'whatever'</span><span class=special>] </span><span class=special>= </span><span class=number>3</span><span class=special>; </span>#<span class=identifier>modifies </span><span class=identifier>the </span><span class=identifier>copy
</span></pre></code>
<a name="class__lt_t_gt__as_objects"></a><h2>class_&lt;T&gt; as objects</h2><p>
Due to the dynamic nature of Boost.Python objects, any <tt>class_&lt;T&gt;</tt> may
also be one of these types! The following code snippet wraps the class
(type) object.</p>
<p>
We can use this to create wrapped instances. Example:</p>
<code><pre>
<span class=identifier>object </span><span class=identifier>vec345 </span><span class=special>= </span><span class=special>(
</span><span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>Vec2</span><span class=special>&gt;(</span><span class=string>&quot;Vec2&quot;</span><span class=special>, </span><span class=identifier>init</span><span class=special>&lt;</span><span class=keyword>double</span><span class=special>, </span><span class=keyword>double</span><span class=special>&gt;())
</span><span class=special>.</span><span class=identifier>def_readonly</span><span class=special>(</span><span class=string>&quot;length&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>Point</span><span class=special>::</span><span class=identifier>length</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def_readonly</span><span class=special>(</span><span class=string>&quot;angle&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>Point</span><span class=special>::</span><span class=identifier>angle</span><span class=special>)
</span><span class=special>)(</span><span class=number>3.0</span><span class=special>, </span><span class=number>4.0</span><span class=special>);
</span><span class=identifier>assert</span><span class=special>(</span><span class=identifier>vec345</span><span class=special>.</span><span class=identifier>attr</span><span class=special>(</span><span class=string>&quot;length&quot;</span><span class=special>) </span><span class=special>== </span><span class=number>5.0</span><span class=special>);
</span></pre></code>
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<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
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<html>
<head>
<!-- Generated by the Spirit (http://spirit.sf.net) QuickDoc -->
<title>Enums</title>
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<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Enums</b></font>
</td>
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</table>
<br>
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<p>
Boost.Python has a nifty facility to capture and wrap C++ enums. While
Python has no <tt>enum</tt> type, we'll often want to expose our C++ enums to
Python as an <tt>int</tt>. Boost.Python's enum facility makes this easy while
taking care of the proper conversions from Python's dynamic typing to C++'s
strong static typing (in C++, ints cannot be implicitly converted to
enums). To illustrate, given a C++ enum:</p>
<code><pre>
<span class=keyword>enum </span><span class=identifier>choice </span><span class=special>{ </span><span class=identifier>red</span><span class=special>, </span><span class=identifier>blue </span><span class=special>};
</span></pre></code>
<p>
the construct:</p>
<code><pre>
<span class=identifier>enum_</span><span class=special>&lt;</span><span class=identifier>choice</span><span class=special>&gt;(</span><span class=string>&quot;choice&quot;</span><span class=special>)
</span><span class=special>.</span><span class=identifier>value</span><span class=special>(</span><span class=string>&quot;red&quot;</span><span class=special>, </span><span class=identifier>red</span><span class=special>)
</span><span class=special>.</span><span class=identifier>value</span><span class=special>(</span><span class=string>&quot;blue&quot;</span><span class=special>, </span><span class=identifier>blue</span><span class=special>)
</span><span class=special>;
</span></pre></code>
<p>
can be used to expose to Python. The new enum type is created in the
current <tt>scope()</tt>, which is usually the current module. The snippet above
creates a Python class derived from Python's <tt>int</tt> type which is
associated with the C++ type passed as its first parameter.</p>
<table width="80%" border="0" align="center">
<tr>
<td class="note_box">
<img src="theme/lens.gif"></img> <b>what is a scope?</b><br><br> The scope is a class that has an
associated global Python object which controls the Python namespace in
which new extension classes and wrapped functions will be defined as
attributes. Details can be found <a href="../../v2/scope.html">
here</a>. </td>
</tr>
</table>
<p>
You can access those values in Python as</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>my_module</span><span class=special>.</span><span class=identifier>choice</span><span class=special>.</span><span class=identifier>red
</span><span class=identifier>my_module</span><span class=special>.</span><span class=identifier>choice</span><span class=special>.</span><span class=identifier>red
</span></pre></code>
<p>
where my_module is the module where the enum is declared. You can also
create a new scope around a class:</p>
<code><pre>
<span class=identifier>scope </span><span class=identifier>in_X</span><span class=special>(</span><span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>X</span><span class=special>&gt;(</span><span class=string>&quot;X&quot;</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def</span><span class=special>( </span><span class=special>... </span><span class=special>)
</span><span class=special>.</span><span class=identifier>def</span><span class=special>( </span><span class=special>... </span><span class=special>)
</span><span class=special>);
</span><span class=comment>// Expose X::nested as X.nested
</span><span class=identifier>enum_</span><span class=special>&lt;</span><span class=identifier>X</span><span class=special>::</span><span class=identifier>nested</span><span class=special>&gt;(</span><span class=string>&quot;nested&quot;</span><span class=special>)
</span><span class=special>.</span><span class=identifier>value</span><span class=special>(</span><span class=string>&quot;red&quot;</span><span class=special>, </span><span class=identifier>red</span><span class=special>)
</span><span class=special>.</span><span class=identifier>value</span><span class=special>(</span><span class=string>&quot;blue&quot;</span><span class=special>, </span><span class=identifier>blue</span><span class=special>)
</span><span class=special>;
</span></pre></code>
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<font size="2">Permission to copy, use, modify, sell and distribute this document
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<title>Exception Translation</title>
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<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Exception Translation</b></font>
</td>
</tr>
</table>
<br>
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<p>
All C++ exceptions must be caught at the boundary with Python code. This
boundary is the point where C++ meets Python. Boost.Python provides a
default exception handler that translates selected standard exceptions,
then gives up:</p>
<code><pre>
<span class=identifier>raise </span><span class=identifier>RuntimeError</span><span class=special>, </span><span class=literal>'unidentifiable C++ Exception'
</span></pre></code>
<p>
Users may provide custom translation. Here's an example:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>PodBayDoorException</span><span class=special>;
</span><span class=keyword>void </span><span class=identifier>translator</span><span class=special>(</span><span class=identifier>PodBayDoorException</span><span class=special>&amp; </span><span class=identifier>x</span><span class=special>) </span><span class=special>{
</span><span class=identifier>PyErr_SetString</span><span class=special>(</span><span class=identifier>PyExc_UserWarning</span><span class=special>, </span><span class=string>&quot;I'm sorry Dave...&quot;</span><span class=special>);
</span><span class=special>}
</span><span class=identifier>BOOST_PYTHON_MODULE</span><span class=special>(</span><span class=identifier>kubrick</span><span class=special>) </span><span class=special>{
</span><span class=identifier>register_exception_translator</span><span class=special>&lt;
</span><span class=identifier>PodBayDoorException</span><span class=special>&gt;(</span><span class=identifier>translator</span><span class=special>);
</span><span class=special>...
</span></pre></code>
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<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
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<title>Exposing Classes</title>
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<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Exposing Classes</b></font>
</td>
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<br>
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<p>
Now let's expose a C++ class to Python.</p>
<p>
Consider a C++ class/struct that we want to expose to Python:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>World
</span><span class=special>{
</span><span class=keyword>void </span><span class=identifier>set</span><span class=special>(</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>msg</span><span class=special>) </span><span class=special>{ </span><span class=keyword>this</span><span class=special>-&gt;</span><span class=identifier>msg </span><span class=special>= </span><span class=identifier>msg</span><span class=special>; </span><span class=special>}
</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>greet</span><span class=special>() </span><span class=special>{ </span><span class=keyword>return </span><span class=identifier>msg</span><span class=special>; </span><span class=special>}
</span><span class=identifier>std</span><span class=special>::</span><span class=identifier>string </span><span class=identifier>msg</span><span class=special>;
</span><span class=special>};
</span></pre></code>
<p>
We can expose this to Python by writing a corresponding Boost.Python
C++ Wrapper:</p>
<code><pre>
<span class=preprocessor>#include </span><span class=special>&lt;</span><span class=identifier>boost</span><span class=special>/</span><span class=identifier>python</span><span class=special>.</span><span class=identifier>hpp</span><span class=special>&gt;
</span><span class=keyword>using </span><span class=keyword>namespace </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>python</span><span class=special>;
</span><span class=identifier>BOOST_PYTHON_MODULE</span><span class=special>(</span><span class=identifier>hello</span><span class=special>)
</span><span class=special>{
</span><span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>World</span><span class=special>&gt;(</span><span class=string>&quot;World&quot;</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;greet&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>World</span><span class=special>::</span><span class=identifier>greet</span><span class=special>)
</span><span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;set&quot;</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>World</span><span class=special>::</span><span class=identifier>set</span><span class=special>)
</span><span class=special>;
</span><span class=special>}
</span></pre></code>
<p>
Here, we wrote a C++ class wrapper that exposes the member functions
<tt>greet</tt> and <tt>set</tt>. Now, after building our module as a shared library, we
may use our class <tt>World</tt> in Python. Here's a sample Python session:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>import </span><span class=identifier>hello
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>planet </span><span class=special>= </span><span class=identifier>hello</span><span class=special>.</span><span class=identifier>World</span><span class=special>()
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>planet</span><span class=special>.</span><span class=identifier>set</span><span class=special>(</span><span class=literal>'howdy'</span><span class=special>)
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>planet</span><span class=special>.</span><span class=identifier>greet</span><span class=special>()
</span><span class=literal>'howdy'
</span></pre></code>
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<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
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<font size="6" face="Verdana, Arial, Helvetica, sans-serif"><b>Extracting C++ objects</b></font>
</td>
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<p>
At some point, we will need to get C++ values out of object instances. This
can be achieved with the <tt>extract&lt;T&gt;</tt> function. Consider the following:</p>
<code><pre>
<span class=keyword>double </span><span class=identifier>x </span><span class=special>= </span><span class=identifier>o</span><span class=special>.</span><span class=identifier>attr</span><span class=special>(</span><span class=string>&quot;length&quot;</span><span class=special>); </span><span class=comment>// compile error
</span></pre></code>
<p>
In the code above, we got a compiler error because Boost.Python
<tt>object</tt> can't be implicitly converted to <tt>double</tt>s. Instead, what
we wanted to do above can be achieved by writing:</p>
<code><pre>
<span class=keyword>double </span><span class=identifier>l </span><span class=special>= </span><span class=identifier>extract</span><span class=special>&lt;</span><span class=keyword>double</span><span class=special>&gt;(</span><span class=identifier>o</span><span class=special>.</span><span class=identifier>attr</span><span class=special>(</span><span class=string>&quot;length&quot;</span><span class=special>));
</span><span class=identifier>Vec2</span><span class=special>&amp; </span><span class=identifier>v </span><span class=special>= </span><span class=identifier>extract</span><span class=special>&lt;</span><span class=identifier>Vec2</span><span class=special>&amp;&gt;(</span><span class=identifier>o</span><span class=special>);
</span><span class=identifier>assert</span><span class=special>(</span><span class=identifier>l </span><span class=special>== </span><span class=identifier>v</span><span class=special>.</span><span class=identifier>length</span><span class=special>());
</span></pre></code>
<p>
The first line attempts to extract the &quot;length&quot; attribute of the
Boost.Python <tt>object</tt> <tt>o</tt>. The second line attempts to <i>extract</i> the
<tt>Vec2</tt> object from held by the Boost.Python <tt>object</tt> <tt>o</tt>.</p>
<p>
Take note that we said &quot;attempt to&quot; above. What if the Boost.Python
<tt>object</tt> <tt>o</tt> does not really hold a <tt>Vec2</tt> type? This is certainly
a possibility considering the dynamic nature of Python <tt>object</tt>s. To
be on the safe side, if the C++ type can't be extracted, an
appropriate exception is thrown. To avoid an exception, we need to
test for extractibility:</p>
<code><pre>
<span class=identifier>extract</span><span class=special>&lt;</span><span class=identifier>Vec2</span><span class=special>&amp;&gt; </span><span class=identifier>x</span><span class=special>(</span><span class=identifier>o</span><span class=special>);
</span><span class=keyword>if </span><span class=special>(</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>check</span><span class=special>()) </span><span class=special>{
</span><span class=identifier>Vec2</span><span class=special>&amp; </span><span class=identifier>v </span><span class=special>= </span><span class=identifier>x</span><span class=special>(); </span><span class=special>...
</span></pre></code>
<p>
<img src="theme/bulb.gif"></img> The astute reader might have noticed that the <tt>extract&lt;T&gt;</tt>
facility in fact solves the mutable copying problem:</p>
<code><pre>
<span class=identifier>dict </span><span class=identifier>d </span><span class=special>= </span><span class=identifier>extract</span><span class=special>&lt;</span><span class=identifier>dict</span><span class=special>&gt;(</span><span class=identifier>x</span><span class=special>.</span><span class=identifier>attr</span><span class=special>(</span><span class=string>&quot;__dict__&quot;</span><span class=special>));
</span><span class=identifier>d</span><span class=special>[</span><span class=literal>'whatever'</span><span class=special>] </span><span class=special>= </span><span class=number>3</span><span class=special>; </span>#<span class=identifier>modifies </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>__dict__ </span><span class=special>!
</span></pre></code>
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<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
is granted provided this copyright notice appears in all copies. This document
is provided &quot;as is&quot; without express or implied warranty, and with
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<title>Functions</title>
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<p>
In this chapter, we'll look at Boost.Python powered functions in closer
detail. We shall see some facilities to make exposing C++ functions to
Python safe from potential pifalls such as dangling pointers and
references. We shall also see facilities that will make it even easier for
us to expose C++ functions that take advantage of C++ features such as
overloading and default arguments.</p>
<blockquote><p><i>Read on...</i></p></blockquote><p>
But before you do, you might want to fire up Python 2.2 or later and type
<tt>&gt;&gt;&gt; import this</tt>.</p>
<code><pre>
&gt;&gt;&gt; import this
The Zen of Python, by Tim Peters
Beautiful is better than ugly.
Explicit is better than implicit.
Simple is better than complex.
Complex is better than complicated.
Flat is better than nested.
Sparse is better than dense.
Readability counts.
Special cases aren't special enough to break the rules.
Although practicality beats purity.
Errors should never pass silently.
Unless explicitly silenced.
In the face of ambiguity, refuse the temptation to guess.
There should be one-- and preferably only one --obvious way to do it
Although that way may not be obvious at first unless you're Dutch.
Now is better than never.
Although never is often better than *right* now.
If the implementation is hard to explain, it's a bad idea.
If the implementation is easy to explain, it may be a good idea.
Namespaces are one honking great idea -- let's do more of those!
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<p>
In the previous examples, we dealt with classes that are not polymorphic.
This is not often the case. Much of the time, we will be wrapping
polymorphic classes and class hierarchies related by inheritance. We will
often have to write Boost.Python wrappers for classes that are derived from
abstract base classes.</p>
<p>
Consider this trivial inheritance structure:</p>
<code><pre>
<span class=keyword>struct </span><span class=identifier>Base </span><span class=special>{ </span><span class=keyword>virtual </span><span class=special>~</span><span class=identifier>Base</span><span class=special>(); </span><span class=special>};
</span><span class=keyword>struct </span><span class=identifier>Derived </span><span class=special>: </span><span class=identifier>Base </span><span class=special>{};
</span></pre></code>
<p>
And a set of C++ functions operating on <tt>Base</tt> and <tt>Derived</tt> object
instances:</p>
<code><pre>
<span class=keyword>void </span><span class=identifier>b</span><span class=special>(</span><span class=identifier>Base</span><span class=special>*);
</span><span class=keyword>void </span><span class=identifier>d</span><span class=special>(</span><span class=identifier>Derived</span><span class=special>*);
</span><span class=identifier>Base</span><span class=special>* </span><span class=identifier>factory</span><span class=special>() </span><span class=special>{ </span><span class=keyword>return </span><span class=keyword>new </span><span class=identifier>Derived</span><span class=special>; </span><span class=special>}
</span></pre></code>
<p>
We've seen how we can wrap the base class <tt>Base</tt>:</p>
<code><pre>
<span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>Base</span><span class=special>&gt;(</span><span class=string>&quot;Base&quot;</span><span class=special>)
</span><span class=comment>/*...*/
</span><span class=special>;
</span></pre></code>
<p>
Now we can inform Boost.Python of the inheritance relationship between
<tt>Derived</tt> and its base class <tt>Base</tt>. Thus:</p>
<code><pre>
<span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>Derived</span><span class=special>, </span><span class=identifier>bases</span><span class=special>&lt;</span><span class=identifier>Base</span><span class=special>&gt; </span><span class=special>&gt;(</span><span class=string>&quot;Derived&quot;</span><span class=special>)
</span><span class=comment>/*...*/
</span><span class=special>;
</span></pre></code>
<p>
Doing so, we get some things for free:</p>
<ol><li>Derived automatically inherits all of Base's Python methods (wrapped C++ member functions)</li><li><b>If</b> Base is polymorphic, <tt>Derived</tt> objects which have been passed to Python via a pointer or reference to <tt>Base</tt> can be passed where a pointer or reference to <tt>Derived</tt> is expected.</li></ol><p>
Now, we shall expose the C++ free functions <tt>b</tt> and <tt>d</tt> and <tt>factory</tt>:</p>
<code><pre>
<span class=identifier>def</span><span class=special>(</span><span class=string>&quot;b&quot;</span><span class=special>, </span><span class=identifier>b</span><span class=special>);
</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;d&quot;</span><span class=special>, </span><span class=identifier>d</span><span class=special>);
</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;factory&quot;</span><span class=special>, </span><span class=identifier>factory</span><span class=special>);
</span></pre></code>
<p>
Note that free function <tt>factory</tt> is being used to generate new
instances of class <tt>Derived</tt>. In such cases, we use
<tt>return_value_policy&lt;manage_new_object&gt;</tt> to instruct Python to adopt
the pointer to <tt>Base</tt> and hold the instance in a new Python <tt>Base</tt>
object until the the Python object is destroyed. We shall see more of
Boost.Python <a href="call_policies.html">
call policies</a> later.</p>
<code><pre>
<span class=comment>// Tell Python to take ownership of factory's result
</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;factory&quot;</span><span class=special>, </span><span class=identifier>factory</span><span class=special>,
</span><span class=identifier>return_value_policy</span><span class=special>&lt;</span><span class=identifier>manage_new_object</span><span class=special>&gt;());
</span></pre></code>
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<p>
In C++, and STL in particular, we see iterators everywhere. Python also has
iterators, but these are two very different beasts.</p>
<p>
<b>C++ iterators:</b></p>
<ul><li>C++ has 5 type categories (random-access, bidirectional, forward, input, output)</li><li>There are 2 Operation categories: reposition, access</li><li>A pair of iterators is needed to represent a (first/last) range.</li></ul><p>
<b>Python Iterators:</b></p>
<ul><li>1 category (forward)</li><li>1 operation category (next())</li><li>Raises StopIteration exception at end</li></ul><p>
The typical Python iteration protocol: <tt><b>for y in x...</b></tt> is as follows:</p>
<code><pre>
<span class=identifier>iter </span><span class=special>= </span><span class=identifier>x</span><span class=special>.</span><span class=identifier>__iter__</span><span class=special>() </span>#<span class=identifier>get </span><span class=identifier>iterator
</span><span class=keyword>try</span><span class=special>:
</span><span class=keyword>while </span><span class=number>1</span><span class=special>:
</span><span class=identifier>y </span><span class=special>= </span><span class=identifier>iter</span><span class=special>.</span><span class=identifier>next</span><span class=special>() </span>#<span class=identifier>get </span><span class=identifier>each </span><span class=identifier>item
</span><span class=special>... </span>#<span class=identifier>process </span><span class=identifier>y
</span><span class=identifier>except </span><span class=identifier>StopIteration</span><span class=special>: </span><span class=identifier>pass </span>#<span class=identifier>iterator </span><span class=identifier>exhausted
</span></pre></code>
<p>
Boost.Python provides some mechanisms to make C++ iterators play along
nicely as Python iterators. What we need to do is to produce
appropriate __iter__ function from C++ iterators that is compatible
with the Python iteration protocol. For example:</p>
<code><pre>
<span class=identifier>object </span><span class=identifier>get_iterator </span><span class=special>= </span><span class=identifier>iterator</span><span class=special>&lt;</span><span class=identifier>vector</span><span class=special>&lt;</span><span class=keyword>int</span><span class=special>&gt; </span><span class=special>&gt;();
</span><span class=identifier>object </span><span class=identifier>iter </span><span class=special>= </span><span class=identifier>get_iterator</span><span class=special>(</span><span class=identifier>v</span><span class=special>);
</span><span class=identifier>object </span><span class=identifier>first </span><span class=special>= </span><span class=identifier>iter</span><span class=special>.</span><span class=identifier>next</span><span class=special>();
</span></pre></code>
<p>
Or for use in class_&lt;&gt;:</p>
<code><pre>
<span class=special>.</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;__iter__&quot;</span><span class=special>, </span><span class=identifier>iterator</span><span class=special>&lt;</span><span class=identifier>vector</span><span class=special>&lt;</span><span class=keyword>int</span><span class=special>&gt; </span><span class=special>&gt;())
</span></pre></code>
<p>
<b>range</b></p>
<p>
We can create a Python savvy iterator using the range function:</p>
<ul><li>range(start, finish)</li><li>range&lt;Policies,Target&gt;(start, finish)</li></ul><p>
Here, start/finish may be one of:</p>
<ul><li>member data pointers</li><li>member function pointers</li><li>adaptable function object (use Target parameter)</li></ul><p>
<b>iterator</b></p>
<ul><li>iterator&lt;T, Policies&gt;()</li></ul><p>
Given a container <tt>T</tt>, iterator is a shortcut that simply calls <tt>range</tt>
with &amp;T::begin, &amp;T::end.</p>
<p>
Let's put this into action... Here's an example from some hypothetical
bogon Particle accelerator code:</p>
<code><pre>
<span class=identifier>f </span><span class=special>= </span><span class=identifier>Field</span><span class=special>()
</span><span class=keyword>for </span><span class=identifier>x </span><span class=identifier>in </span><span class=identifier>f</span><span class=special>.</span><span class=identifier>pions</span><span class=special>:
</span><span class=identifier>smash</span><span class=special>(</span><span class=identifier>x</span><span class=special>)
</span><span class=keyword>for </span><span class=identifier>y </span><span class=identifier>in </span><span class=identifier>f</span><span class=special>.</span><span class=identifier>bogons</span><span class=special>:
</span><span class=identifier>count</span><span class=special>(</span><span class=identifier>y</span><span class=special>)
</span></pre></code>
<p>
Now, our C++ Wrapper:</p>
<code><pre>
<span class=identifier>class_</span><span class=special>&lt;</span><span class=identifier>F</span><span class=special>&gt;(</span><span class=string>&quot;Field&quot;</span><span class=special>)
</span><span class=special>.</span><span class=identifier>property</span><span class=special>(</span><span class=string>&quot;pions&quot;</span><span class=special>, </span><span class=identifier>range</span><span class=special>(&amp;</span><span class=identifier>F</span><span class=special>::</span><span class=identifier>p_begin</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>F</span><span class=special>::</span><span class=identifier>p_end</span><span class=special>))
</span><span class=special>.</span><span class=identifier>property</span><span class=special>(</span><span class=string>&quot;bogons&quot;</span><span class=special>, </span><span class=identifier>range</span><span class=special>(&amp;</span><span class=identifier>F</span><span class=special>::</span><span class=identifier>b_begin</span><span class=special>, </span><span class=special>&amp;</span><span class=identifier>F</span><span class=special>::</span><span class=identifier>b_end</span><span class=special>));
</span></pre></code>
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<p>
Python is dynamically typed, unlike C++ which is statically typed. Python
variables may hold an integer, a float, list, dict, tuple, str, long etc.,
among other things. In the viewpoint of Boost.Python and C++, these
Pythonic variables are just instances of class <tt>object</tt>. We shall see in
this chapter how to deal with Python objects.</p>
<p>
As mentioned, one of the goals of Boost.Python is to provide a
bidirectional mapping between C++ and Python while maintaining the Python
feel. Boost.Python C++ <tt>object</tt>s are as close as possible to Python. This
should minimize the learning curve significantly.</p>
<p>
<img src="theme/python.png"></img></p>
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<p>
The Boost Python Library is a framework for interfacing Python and
C++. It allows you to quickly and seamlessly expose C++ classes
functions and objects to Python, and vice-versa, using no special
tools -- just your C++ compiler. It is designed to wrap C++ interfaces
non-intrusively, so that you should not have to change the C++ code at
all in order to wrap it, making Boost.Python ideal for exposing
3rd-party libraries to Python. The library's use of advanced
metaprogramming techniques simplifies its syntax for users, so that
wrapping code takes on the look of a kind of declarative interface
definition language (IDL).</p>
<a name="hello_world"></a><h2>Hello World</h2><p>
Following C/C++ tradition, let's start with the &quot;hello, world&quot;. A C++
Function:</p>
<code><pre>
<span class=keyword>char </span><span class=keyword>const</span><span class=special>* </span><span class=identifier>greet</span><span class=special>()
</span><span class=special>{
</span><span class=keyword>return </span><span class=string>&quot;hello, world&quot;</span><span class=special>;
</span><span class=special>}
</span></pre></code>
<p>
can be exposed to Python by writing a Boost.Python wrapper:</p>
<code><pre>
<span class=preprocessor>#include </span><span class=special>&lt;</span><span class=identifier>boost</span><span class=special>/</span><span class=identifier>python</span><span class=special>.</span><span class=identifier>hpp</span><span class=special>&gt;
</span><span class=keyword>using </span><span class=keyword>namespace </span><span class=identifier>boost</span><span class=special>::</span><span class=identifier>python</span><span class=special>;
</span><span class=identifier>BOOST_PYTHON_MODULE</span><span class=special>(</span><span class=identifier>hello</span><span class=special>)
</span><span class=special>{
</span><span class=identifier>def</span><span class=special>(</span><span class=string>&quot;greet&quot;</span><span class=special>, </span><span class=identifier>greet</span><span class=special>);
</span><span class=special>}
</span></pre></code>
<p>
That's it. We're done. We can now build this as a shared library. The
resulting DLL is now visible to Python. Here's a sample Python session:</p>
<code><pre>
<span class=special>&gt;&gt;&gt; </span><span class=identifier>import </span><span class=identifier>hello
</span><span class=special>&gt;&gt;&gt; </span><span class=identifier>print </span><span class=identifier>hello</span><span class=special>.</span><span class=identifier>greet</span><span class=special>()
</span><span class=identifier>hello</span><span class=special>, </span><span class=identifier>world
</span></pre></code>
<blockquote><p><i><b>Next stop... Building your Hello World module from start to finish...</b></i></p></blockquote><table border="0">
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<font size="2">Permission to copy, use, modify, sell and distribute this document
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<a href="doc/object_interface.html">Object Interface</a>
</td>
</tr>
<tr>
<td class="toc_cells_L1">
<a href="doc/basic_interface.html">Basic Interface</a>
</td>
</tr>
<tr>
<td class="toc_cells_L1">
<a href="doc/derived_object_types.html">Derived Object types</a>
</td>
</tr>
<tr>
<td class="toc_cells_L1">
<a href="doc/extracting_c___objects.html">Extracting C++ objects</a>
</td>
</tr>
<tr>
<td class="toc_cells_L1">
<a href="doc/enums.html">Enums</a>
</td>
</tr>
<tr>
<td class="toc_cells_L0">
<a href="doc/iterators.html">Iterators</a>
</td>
</tr>
<tr>
<td class="toc_cells_L0">
<a href="doc/exception_translation.html">Exception Translation</a>
</td>
</tr>
</table>
<br>
<hr size="1"><p class="copyright">Copyright &copy; 2002 David Abrahams<br>Copyright &copy; 2002 Joel de Guzman<br><br>
<font size="2">Permission to copy, use, modify, sell and distribute this document
is granted provided this copyright notice appears in all copies. This document
is provided &quot;as is&quot; without express or implied warranty, and with
no claim as to its suitability for any purpose. </font> </p>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - April 2002 Progress Report</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">April 2002 Progress Report</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="index">
<dt><a href="#accomplishments">Accomplishments</a></dt>
<dl class="index">
<dt><a href="#arity">Arbitrary Arity Support</a></dt>
<dt><a href="#callbacks">New Callback Interface</a></dt>
<dt><a href="#policies">Call Policies for Construtors</a></dt>
<dt><a href="#bugs">Real Users, Real Bugs</a></dt>
<dt><a href="#insights">New Insights</a></dt>
<dt><a href="#v1">Boost.Python V1 Maintenance</a></dt>
</dl>
<dt><a href="#missing">What's Missing</a></dt>
</dl>
<h2><a name="accomplishments">Accomplishments</a></h2>
April was a short month as far as Boost.Python was concerned, since
the spring ISO C++ Committee Meeting (and associated vacation)
occupied me for the 2nd half of the month. However, a suprising amount
of work got done...
<h3><a name="arity">Arbitrary Arity Support</a></h3>
I began using the <a
href="../../../preprocessor/doc/index.htm">Boost.Preprocessor</a>
metaprogramming library to generate support for functions and member
functions of arbitrary arity, which was, to say the least, quite an
adventure. The feedback cycle resulting from my foray into
Boost.Preprocessor resulted in several improvements to the library,
most notably in its documentation.
<p>
Boost.Python now supports calls of up to 17 arguments on most
compilers. Because most EDG-based compilers have dismal preprocessor
performance, I had to &quot;manually&quot; expand the metaprograms for
arities from zero to fifteen arguments, and EDG-based compilers with
<code>__EDG_VERSION__&nbsp;&lt;=&nbsp;245</code> only support 15
arguments by default. If some crazy program finds a need for more than
the default arity support, users can increase the base support by
setting the <code>BOOST_PYTHON_MAX_ARITY</code> preprocessor symbol.
<h3><a name="callbacks">New Callback Interface</a></h3>
I mentioned in <a href="Mar2002.html">last month's report</a> that I
wasn't pleased with the interface for the interface for calling into
Python, so now it has been redesigned. The new interface is outlined
in <a
href="http://mail.python.org/pipermail/c++-sig/2002-April/000953.html">this
message</a> (though the GCC 2.95.3 bugs have been fixed).
<h3><a name="policies">Call Policies for Constructors</a></h3>
On April 2nd, I <a
href="http://mail.python.org/pipermail/c++-sig/2002-April/000916.html">announced</a>
support for the use of call policies with constructors.
<h3><a name="bugs">Real Users, Real Bugs</a></h3>
At least two people outside of Kull began actually using Boost.Python
v2 in earnest this month. Peter Bienstman and Pearu Pearson both
provided valuable real-world bug reports that helped me to improve the
library's robustness.
<h3><a name="insights">New Insights</a></h3>
<a
href="http://mail.python.org/pipermail/c++-sig/2002-May/001010.html"
>Answering some of Pearu's questions</a> about explicitly converting
objects between Python and C++ actually led me to a new understanding
of the role of the current conversion facilities. In Boost.Python v1,
all conversions between Python and C++ were handled by a single family
of functions, called <code>to_python()</code> and
<code>from_python()</code>. Since the primary role of Boost.Python is
to wrap C++ functions in Python, I used these names for the first kind
of converters I needed: those that extract C++ objects to be used as
function arguments and which C++ function return values to
Python. The better-considered approach in Boost.Python v2 uses a
completely different mechanism for conversions used when calling
Python from C++, as in wrapped virtual function implementations. I
usually think of this as a &quot;callback&quot;, as in &quot;calling
back into Python&quot;, and I named the converters used in callbacks
accordingly: <code>to_python_callback</code> and
<code>from_python_callback</code>. However, as it turns out, the
behavior of the &quot;callback&quot; converters is the appropriate one
for users who want to explicitly extract a C++ value from a Python
object, or create a Python object from a C++ value. The upshot is that
it probably makes sense to change the name of the existing <code>to_python</code> and
<code>from_python</code> so those names are available for the
user-friendly explicit converters.
<p>
<a
href="http://mail.python.org/pipermail/c++-sig/2002-May/001013.html">Another
of Pearu's questions</a> pushes momentum further in the direction of a
more-sophisticated overloading mechanism than the current
simple-minded &quot;first match&quot; approach, as I suggested <a
href="Mar2002.html#implicit_conversions">last month</a>.
<h3><a name="v1">Boost.Python V1 Maintenance</a></h3>
As much as I'm looking forward to retiring Boost.Python v1, a
significant amount of effort has been being spent dealing with support
problems; the saying that code rots when left alone is true, and
Boost.Python is no exception. Eventually it became obvious to me that
we were going to have to invest some effort in keeping V1 healthy
while working on V2. Ralf and I have expanded support for various
compilers and stabilized the V1 codebase considerably. We discarded
the obsolete Visual Studio projects which were causing so much
confusion. Still to do before the next Boost release:
<ol>
<li>Update the build/test documentation with detailed instructions for
configuring various toolsets.
<li>Provide some links to Boost.Python v2 to let people know what's
coming.
</ol>
<h2><a name="missing">What's Missing</a></h2>
Last month I announced that I would implement the following which are
not yet complete:
<ol>
<li>Document all implemented features
<li>Implement conversions for <code>char</code> types. This is
implemented but not tested, so we have to assume it doesn't work.
</ol>
These are my first priority for this month (especially the
documentation).
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
3 May, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a>
2002. All Rights Reserved.</i></p>
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../../../boost.css">
<title>Boost.Python - CallPolicies Concept</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">CallPolicies Concept</h2>
</td>
</tr>
</table>
<hr>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#composition">CallPolicies Composition</a></dt>
<dt><a href="#concept-requirements">Concept Requirements</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#CallPolicies-concept">CallPolicies Concept</a></dt>
</dl>
</dd>
</dl>
<h2><a name="introduction"></a>Introduction</h2>
<p>Models of the CallPolicies concept are used to specialize the behavior
of Python callable objects generated by Boost.Python to wrapped C++
objects like function and member function pointers, providing three
behaviors:</p>
<ol>
<li><code>precall</code> - Python argument tuple management before the
wrapped object is invoked</li>
<li><code>result_converter</code> - C++ return value handling</li>
<li><code>postcall</code> - Python argument tuple and result management
after the wrapped object is invoked</li>
</ol>
<h2><a name="composition"></a>CallPolicies Composition</h2>
In order to allow the use of multiple models of CallPolicies in the same
callable object, Boost.Python's CallPolicies class templates provide a
chaining interface which allows them to be recursively composed. This
interface takes the form of an optional template parameter,
<code>Base</code> which defaults to <a href=
"default_call_policies.html#default_call_policies-spec"><code>default_call_policies</code></a>.
By convention, the <code>precall</code> function of the <code>Base</code>
is invoked <i>after</i> the <code>precall</code> function supplied by the
outer template, and the <code>postcall</code> function of the
<code>Base</code> is invoked <i>before</i> the <code>postcall</code>
function of the outer template. If a <code>result_converter</code> is
supplied by the outer template, it <i>replaces</i> any
<code>result_converter</code> supplied by the <code>Base</code>. For an
example, see <a href=
"return_internal_reference.html#return_internal_reference-spec"><code>return_internal_reference</code></a>.
<h2><a name="concept-requirements"></a>Concept Requirements</h2>
<h3><a name="CallPolicies-concept"></a>CallPolicies Concept</h3>
<p>In the table below, <code><b>x</b></code> denotes an object whose type
<code><b>P</b></code> is a model of CallPolicies, <code><b>a</b></code>
denotes a <code>PyObject*</code> pointing to a Python argument tuple
object, and <code><b>r</b></code> denotes a <code>PyObject*</code>
referring to a "preliminary" result object.</p>
<table summary="CallPolicies expressions" border="1" cellpadding="5">
<tr>
<td><b>Expression</b></td>
<td><b>Type</b></td>
<td><b>Result/Semantics</b></td>
</tr>
<tr>
<td valign="top"><code>x.precall(a)</code></td>
<td>convertible to <code>bool</code></td>
<td>returns <code>false</code> and <code><a href=
"http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71">PyErr_Occurred</a>()&nbsp;!=&nbsp;0</code>
upon failure, <code>true</code> otherwise.</td>
</tr>
<tr>
<td valign="top"><code>P::result_converter</code></td>
<td>A model of <a href=
"ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a>.</td>
<td>An MPL unary <a href=
"../../../mpl/doc/paper/html/usage.html#metafunctions.classes">Metafunction
Class</a> used produce the "preliminary" result object.</td>
</tr>
<tr>
<td valign="top"><code>x.postcall(a, r)</code></td>
<td>convertible to <code>PyObject*</code></td>
<td>0 <code>0</code> and <code><a href=
"http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71">PyErr_Occurred</a>()&nbsp;!=&nbsp;0</code>
upon failure. Must "conserve references" even in the event of an
exception. In other words, if <code>r</code> is not returned, its
reference count must be decremented; if another existing object is
returned, its reference count must be incremented.</td>
</tr>
</table>
Models of CallPolicies are required to be <a href=
"../../../utility/CopyConstructible.html">CopyConstructible</a>.
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
19 May, 2002 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
<p>Permission to copy, use, modify, sell and distribute this software is
granted provided this copyright notice appears in all copies. This
software is provided "as is" without express or implied warranty, and
with no claim as to its suitability for any purpose.</p>
</body>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../../../boost.css">
<title>Boost.Python - Dereferenceable Concept</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Dereferenceable Concept</h2>
</td>
</tr>
</table>
<hr>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#concept-requirements">Concept Requirements</a></dt>
<dl class="page-index">
<dt><a href="#Dereferenceable-concept">Dereferenceable Concept</a></dt>
</dl>
</dl>
<h2><a name="introduction"></a>Introduction</h2>
<p>Instances of a dereferenceable type can be used like a pointer to access an lvalue.
<h2><a name="concept-requirements"></a>Concept Requirements</h2>
<h3><a name="Dereferenceable-concept"></a>Dereferenceable Concept</h3>
<p>In the table below, <code><b>x</b></code> denotes an object whose
type is a model of Dereferenceable.
<table summary="Dereferenceable expressions" border="1" cellpadding="5">
<tr>
<td><b>Expression</b></td>
<td><b>Requirements</b></td>
</tr>
<tr>
<td valign="top"><code>*x</code></td>
<td>An lvalue
</tr>
</table>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
10 May, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>
<p>Permission to copy, use, modify, sell
and distribute this software is granted provided this copyright notice appears
in all copies. This software is provided "as is" without express or implied
warranty, and with no claim as to its suitability for any purpose.
</body>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../../../boost.css">
<title>Boost.Python - Extractor Concept</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Extractor Concept</h2>
</td>
</tr>
</table>
<hr>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#concept-requirements">Concept Requirements</a></dt>
<dl class="page-index">
<dt><a href="#Extractor-concept">Extractor Concept</a></dt>
</dl>
<dt><a href="#notes">Notes</a></dt>
</dl>
<h2><a name="introduction"></a>Introduction</h2>
<p>An Extractor is a class which Boost.Python can use to extract C++
objects from Python objects, and is typically used by facilities that
define <code>from_python</code> conversions for
&quot;traditional&quot; Python extension types.
<h2><a name="concept-requirements"></a>Concept Requirements</h2>
<h3><a name="Extractor-concept"></a>Extractor Concept</h3>
<p>In the table below, <code><b>X</b></code> denotes a model of
Extractor and <code><b>a</b></code> denotes an instance of a Python
object type.
<table summary="Extractor expressions" border="1" cellpadding="5">
<tr>
<td><b>Expression</b></td>
<td><b>Type</b></td>
<td><b>Semantics</b></td>
</tr>
<tr>
<td valign="top"><code>X::execute(a)</code></td>
<td>non-void
<td>Returns the C++ object being extracted. The
<code>execute</code> function must not be overloaded.
</tr>
<tr>
<td valign="top"><code>&amp;a.ob_type</code>
<td><code><a
href="http://www.python.org/doc/2.2/ext/dnt-type-methods.html">PyTypeObject</a>**</code>
<td>Points to the <code>ob_type</code> field of an object which is
layout-compatible with <code>PyObject</code>
</tr>
</tr>
</table>
<h2><a name="notes"></a>Notes</h2>
Informally, an Extractor's <code>execute</code> member must be a
non-overloaded static function whose single argument is a Python
object type. Acceptable Python object types include those publicly (and
unambiguously) derived from <code>PyObject</code>, and POD types which
are layout-compatible with PyObject.
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
22 May, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>
<p>Permission to copy, use, modify, sell
and distribute this software is granted provided this copyright notice appears
in all copies. This software is provided "as is" without express or implied
warranty, and with no claim as to its suitability for any purpose.
</body>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../../../boost.css">
<title>Boost.Python - Holder Concept</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">HolderGenerator Concept</h2>
</td>
</tr>
</table>
<hr>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#concept-requirements">Concept Requirements</a></dt>
<dl class="page-index">
<dt><a href="#HolderGenerator-concept">HolderGenerator Concept</a></dt>
</dl>
</dl>
<h2><a name="introduction"></a>Introduction</h2>
<p>A HolderGenerator is a unary metafunction class which returns types
suitable for holding instances of its argument in a wrapped C++ class
instance.
<h2><a name="concept-requirements"></a>Concept Requirements</h2>
<h3><a name="HolderGenerator-concept"></a>HolderGenerator Concept</h3>
<p>In the table below, <code><b>G</b></code> denotes an type which
models HolderGenerator, and <code><b>X</b></code> denotes a class
type.
<table summary="Holder expressions" border="1" cellpadding="5">
<tr>
<td><b>Expression</b></td>
<td><b>Requirements</b></td>
</tr>
<tr>
<td valign="top"><code>G::apply&lt;X&gt;::type</code></td>
<td>A concrete subclass of <a
href="instance_holder.html#instance_holder-spec">instance_holder</a>
which can hold objects of type <code>X</code>.
</tr>
</table>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
20 May, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>
<p>Permission to copy, use, modify, sell
and distribute this software is granted provided this copyright notice appears
in all copies. This software is provided "as is" without express or implied
warranty, and with no claim as to its suitability for any purpose.
</body>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - June 2002 Progress Report</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">June 2002 Progress Report</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="index">
<dt><a href="#intro">Introduction</a></dt>
<dt><a href="#handle"><code>handle&lt;T&gt;</code></a></dt>
<dt><a href="#object"><code>object</code></a></dt>
<dl class="index">
<dt><a href="#operators"><code>object</code> operators</a></dt>
<dt><a href="#conversions"><code>object</code> conversions</a></dt>
</dl>
<dt><a href="#list"><code>list</code></a></dt>
<dt><a href="#numerics"><code>Numerics</code></a></dt>
<dt><a href="#community">Community</a></dt>
<dt><a href="#next">What's Next</a></dt>
</dl>
<h2><a name="intro">Introduction</a></h2>
July was mostly focused on allowing expressive manipulation of
individual Python objects, or what Ralf Grosse-Kunstleve calls
&quot;Writing Python in C++&quot;. The work began with this <a
href="http://mail.python.org/pipermail/c++-sig/2002-June/001311.html">posting</a>,
which outlines the issues and intention.
<h2><a name="handle"><code>handle&lt;T&gt;</code></a></h2>
The most basic element needed was a replacement for the
<code>reference&lt;&gt;</code> class template and the
<code>ref</code> typedef from Boost.Python v1, a simple smart
pointer to a Python object. The old v1 typedef
&quot;<code>ref</code>&quot; (for
<code>reference&lt;PyObject&gt;</code>) had to be retired because I
thought it would be too confusing given the importance of <code><a
href="../../../bind/ref.html">boost::ref</a>()</code> to this
library. I began a <a
href="http://mail.python.org/pipermail/c++-sig/2002-June/001311.html">discussion</a>of
possible names, and it was eventually <a
href="http://mail.python.org/pipermail/c++-sig/2002-June/001337.html">decided</a>
to rename <code>reference</code> to <code>handle</code> and supply a
default argument so that <code>ref</code> could be spelled
<code>handle&lt;&gt;</code> without an additional typedef. There
were also some interface changes to make it safer and more-efficient
to interface with the raw
<code>PyObject*</code>s forced on us by Python's 'C' API. A
discussion of those protocols can be found <a
href="http://mail.python.org/pipermail/c++-sig/2002-June/001401.html">here</a>.
<h2><a name="handle"><code>object</code></a></h2>
It is intended that users will seldom need or want to work with
<code>handle&lt;&gt;</code>; its major distinguishing features are
that it gives direct access to the underlying object representation
through <code>operator*</code> and <code>operator-&gt;</code>, and
that can be <code>NULL</code>, both sources of danger. Instead the
library provides a class called <code>object</code>, which
encapsulates a valid Python object and provides a similar interface to
Python's.
<h3><a name="operators"><code>object</code> operators</a></h3>
The first challenge was to provide support for object manipulations
using a Python-like syntax, mostly in the form of operator overloads:
<table border="1">
<tr><th>Python <th>C++
<tr>
<td><code>y = x.foo</code> <td><code>y = x.attr(&quot;foo&quot;);
<tr>
<td><code>x.foo = 1</code> <td><code>x.attr(&quot;foo&quot;) = 1;
<tr>
<td><code>y = x[z]</code> <td><code>y = x[z];
<tr>
<td><code>x[z] = 1</code> <td><code>x[z] = 1;
<tr>
<td><code>y = x[3:-1]</code> <td><code>y = x.slice(3,-1);
<tr>
<td><code>y = x[3:]</code> <td><code>y = x.slice(3,_);
<tr>
<td><code>y = x[:-2]</code> <td><code>y = x.slice(_,-2);
<tr>
<td><code>z = x(1, y)</code> <td><code>z = x(1, y);
<tr>
<td><code>z = x.f(1, y)</code> <td><code>z = x.attr(&quot;f&quot;)(1, y);
<tr>
<td><code>not x</code> <td><code>!x
<tr>
<td><code>x and y</code> <td><code>x and y
</table>
I'm still a unsatisfied with the interface for attribute access. There
original proposal used a syntax like this one:
<pre>
y = x._(&quot;foo&quot;);
x._(&quot;foo&quot;) = 1;
</pre>
which was only marginally better than what we've got. Niki Spahiev
then <a
href="http://mail.python.org/pipermail/c++-sig/2002-June/001447.html">pointed
out</a> a potential conflict with the macro which GNU Gettext <a
href="http://www.gnu.org/manual/gettext/html_mono/gettext.html#SEC6">suggests</a>
people define. This unfortunate state of affairs forced us into using
<code>attr</code> instead. I'd still like to find a better interface,
but the lack of overloadable C++ operators which aren't already used
in Python is an obstacle. The comma operator is still a possibility,
but it has the wrong precedence:
<pre>
y = x,&quot;foo&quot; // error
x,&quot;foo&quot; = 1; // error
y = (x,&quot;foo&quot;); // ok
(x,&quot;foo&quot;) = 1; // ok
</pre>
Well, I guess we could consider adding that to the interface without
removing <code>attr()</code>, to see how it plays out...
<h3><a name="operators"><code>object</code> conversions</a></h3>
The <code>object</code> class also provided an opportunity to replace
Boost.Python v1's <code>to_python()</code> as a user-level
interface. Instead, <code>object</code> has a templated constructor
which can be used to convert any C++ object to Python using the same
underlying mechanisms used for the arguments to <code><a
href="call.html">call</a>&lt;&gt;</code>.
<p>Incidentally, the implementation of operator and conversion support
for object uncovered an inordinate number of compiler bugs in our
targeted platforms. It was a lot more &quot;interesting&quot; than it
should have been.
<h2><a name="list"><code>list</code></a></h2>
With <code>object</code> implemented, it was time to begin replacing
the ad-hoc implementations of <code>list</code>, <code>string</code>,
and <code>dictionary</code> supplied by Boost.Python v1 with something
more robust. I started with <code>list</code> as an example. Because
<code>object</code> already provides all of the requisite operators,
publicly deriving <code>list</code> from object seemed like a good
choice. The remaining issues were what do do about the one-argument
list constructor (which in Python attempts to convert its argument to
a list), and how to deal converting with <code>list</code> arguments
to wrapped functions. Some of the issues are laid out in <a
href="http://mail.python.org/pipermail/c++-sig/2002-June/001551.html">this
thread</a>. Ultimately, it was decided that <code>list(x)</code>
should do the same thing in C++ as in Python (conversion), while
<code>list</code> arguments should only match Python
<code>list</code>s (and <code>list</code> subclasses). The
implementation worked well, and provided a <a
href="http://mail.python.org/pipermail/c++-sig/2002-June/001586.html">roadmap</a>
for the protocol to be used for implementation of the other built-in
types.
<h2><a name="numerics">Numerics</a></h2>
Support for C++ <code>long long</code> and <code>unsigned long
long</code>
(and <code>__int64</code> on MSVC) to/from python conversions was
added this month. We also improved handling of numeric overflows when
converting, e.g., a Python int to a type with a more limited range of
representation.
<h2><a name="community">Community</a></h2>
<ul>
<li>Ralf W. Grosse-Kunstleve and Nick Sauter have implemented
<a href="http://cci.lbl.gov/boost/">multiplatform nightly
build-and-test</a> runs for Boost.Python V2 at LBL.
<li>Dave Hawkes has made significant progress on generating the
Python <a
href="http://mail.python.org/pipermail/c++-sig/2002-June/001503.html">built-in
function and API wrappers</a>
<li>Achim Domma has agreed to take up the job of implementing the
<code>str</code>, <code>dict</code>, and <code>tuple</code> classes.
</ul>
Deep thanks to all the Boost.Python contributors! This project
wouldn't be possible without your participation.
<h2><a name="next">What's Next</a></h2>
As I write this we are already well into the month of July, so I
suggest you consult the <a
href="http://mail.python.org/pipermail/c++-sig/2002-July/">Mailing
List Archive</a> if you want to know what's been happening. Otherwise
you'll just have to wait till next month (hopefully the beginning).
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
19 July, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a>
2002. All Rights Reserved.</i></p>
</body>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - March 2002 Progress Report</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">March 2002 Progress Report</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="index">
<dt><a href="#accomplishments">Accomplishments</a></dt>
<dl class="index">
<dt><a href="#calling_python">Calling Python from C++</a></dt>
<dt><a href="#virtual_functions">Virtual Functions</a></dt>
<dt><a href="#abstract_classes">Abstract Classes</a></dt>
<dt><a href="#implicit_conversions">C++ Implicit Conversions</a></dt>
<dt><a href="#data_members">C++ Data Members</a></dt>
<dt><a href="#miscellaneous">Miscellaneous</a></dt>
</dl>
<dt><a href="#future">The Near future</a></dt>
<dt><a href="#notes">Notes</a></dt>
</dl>
<h2><a name="accomplishments">Accomplishments</a></h2>
March was mostly devoted to the reimplementation of features from
Boost.Python v1, and some new features. Re-examination of the features
from Boost.Python v1 allowed me to make significant improvements.
<h3><a name="calling_python">Calling Python from C++</a></h3>
The ability to call Python from C++ is crucial for virtual function
support. Implementing this feature well for V2 proved to be more
interesting than I expected. You can review most of the relevant
design decisions
<a href="callbacks.txt">here</a>.
<p>
One point which <i>isn't</i> emphasized in that document is that there
are subtle differences in the way <code>from_python</code> conversions
work when used for C++ function arguments and Python function return
values. In particular, while <code>T const&amp;</code> arguments may
invoke rvalue converters, a reference-to-const return value requires
an lvalue converter, since a temporary conversion result would leave
the returned reference dangling.
<p>I'm not particularly pleased with the current callback interface,
since it usually results in constructs like:
<pre>
<u>return returning</u>&lt;X&amp;&gt;::call(f, obj);
</pre>
However, I think the following may be possible and I plan to investigate:
<pre>
return apply&lt;X&amp;&gt;(f, obj);
</pre>
I'm open to suggestion for better names (and syntaxes)!
<h3><a name="virtual_functions">Virtual Functions</a></h3>
Once Python callbacks were implemented, it was just a short step to
implementing virtual functions. Python extension class exposing a C++
class whose virtual functions are overridable in Python must actually
hold a C++ instance of a class <i>derived</i> from the one exposed to
Python. Needing some way for users to specify that class, I added an
optional template argument to <code>value_holder_generator</code> and
<code>pointer_holder_generator&lt;&gt;</code> to specify the class
actually held. This move began to put pressure on the
<code>class_&lt;&gt;</code> interface, since the need for the user to
produce complicated instantations of
<code>class_&lt;&gt;</code> was increased:
<pre>
class&lt;Foo, bases&lt;&gt;, value_holder_generator&lt;Foo_callback&gt; &gt;(&quot;Foo&quot;)
.def(&quot;hello&quot;, &amp;Foo::hello)
...
</pre>
<h3><a name="abstract_classes">Abstract Classes</a></h3>
Normally when a C++ class is exposed to Python, the library registers
a conversion function which allows users to wrap functions returning
values of that type. Naturally, these return values are temporaries,
so the conversion function must make a copy in some
dynamically-allocated storage (a &quot;holder&quot;) which is managed
by the corresponding Python object.
<p>Unfortunately, in the case of abstract classes (and other types
without a publicly-accessible copy constructor), instantiating this
conversion function causes a compilation error. In order to support
non-copyable classes, there had to be some way to prevent the library
from trying to instantiate the conversion function. The only practical
approach I could think of was to add an additional template parameter
to the <code>class_&lt;&gt;</code> interface. When the number of
template parameters with useful defaults begins to grow, it is often
hard to choose an order which allows users to take advantage of the
defaults.
<p>
This was the straw that broke the
<code>class_&lt;&gt;</code> interface's back and caused the redesign
whose outcome is detailed <a
href="http://mail.python.org/pipermail/c++-sig/2002-March/000892.html">here</a>.
The approach allows the user to supply the optional parameters in an
arbitrary order. It was inspired by the use of <a
href="../../../utility/iterator_adaptors.htm#named_tempalte_parameters">named
template parameters</a> in the <a
href="../../../utility/iterator_adaptors.htm">Boost Iterator Adaptor
Library</a>, though in this case it is possible to deduce the meaning
of the template parameters entirely from their type properties,
resulting in a simpler interface. Although the move from a
policy-based design to what resembles a configuration DSL usually
implies a loss of flexibility, in this case I think any costs are far
outweighed by the advantages.
<p>Note: working around the limitations of the various compilers I'm
supporting was non-trivial, and resulted in a few messy implementation
details. It might be a good idea to switch to a more-straightforward
approach once Metrowerks CodeWarrior Pro8 is released.
<h3><a name="implicit_conversions">C++ Implicit Conversions</a></h3>
Support for C++ implicit conversion involves creating
<code>from_python</code> converters for a type <code>U</code> which in
turn use <code>from_python</code> converters registered for a type
<code>T</code> where there exists a implicit conversion from
<code>T</code> to <code>U</code>. The current implementation is
subject to two inefficiencies:
<ol>
<li>Because an rvalue <code>from_python</code> converter produces two
pieces of data (a function and a <code>void*</code>) from its
<code>convertible()</code> function, we end up calling the function
for <code>T</code> twice: once when the converter is looked up in the
registry, and again when the conversion is actually performed.
<li>A vector is used to mark the "visited" converters, preventing
infinite recursion as <code>T</code> to
<code>U</code> and <code>U</code> to <code>T</code> converters
continually search through one-another.
</ol>
I consider the former to be a minor issue. The second may or may not
prove to be computationally significant, but I believe that
architecturally, it points toward a need for more sophisticated
overload resolution. It may be that we want CLOS-style multimethod
dispatching along with C++ style rules that prevent more than one
implicit conversion per argument.
<h3><a name="data_members">C++ Data Members</a></h3>
To supply the ability to directly access data members, I was able to
hijack the new Python <a
href="http://www.python.org/2.2/descrintro.html#property">property</a>
type. I had hoped that I would also be able to re-use the work of <a
href="make_function.html">make_function</a> to create callable python
objects from C++ functions which access a data member of a given
class. C++ facilities for specifying data member pointer non-type
template arguments require the user to explicitly specify the type of
the data member and this under-utilized feature is also not
well-implemented on all compilers, so passing the member pointer as a
runtime value is the only practical approach. The upshot is that any
such entity would actually have to be a function <i>object</i>, and I
haven't implemented automatic wrapping of C++ callable function
objects yet, so there is less re-use in the implementation than I'd
like. I hope to implement callable object wrapping and refactor this
code one day. I also hope to implement static data member support,
for which Python's property will not be an appropriate descriptor.
<h3><a name="miscellaneous">Miscellaneous</a></h3>
<ul>
<li>Moved <code>args&lt;&gt;</code> and <code>bases&lt;&gt;</code> from unnamed namespace to <code>boost::python</code> in their own header files.
<li>Convert <code>NULL</code> pointers returned from wrapped C++ functions to <code>None</code>.
<li>Improved some compile-time error checks.
<li>Eliminated <code>boost/python/detail/eval.hpp</code> in favor of
more-general <code>boost/mpl/apply.hpp</code>.
<li>General code cleanup and refactoring.
<li>Works with Microsoft Visual C++ 7.0
<li>Warning suppression for many compilers
<li>Elegant interface design for exporting <code>enum</code> types.
</ul>
<hr>
<h2><a name="future">The Near Future</a></h2>
Before April 15th I plan to
<ol>
<li>Document all implemented features
<li>Implement a <code>CallPolicy</code> interface for constructors of wrapped
classes
<li>Implement conversions for <code>char</code> types.
<li>Implement automated code generation for all headers containing
families of overloaded functions to handle arbitrary arity.
</ol>
I also hope to implement a mechanism for generating conversions
between arbitrary Python sequences and C++ containers, if time permits
(and others haven't already done it)!
<h2><a name="notes">Notes</a></h2>
The older version of KCC used by Kull is generating lots of warnings
about a construct I use to instantiate static members of various class
templates. I'm thinking of moving to an idiom which uses a function
template to suppress it, but worry about bloating the size of debug
builds. Since KCC users may be moving to GCC, I'm not sure that it's
worth doing anything about it.
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
1 April, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a>
2002. All Rights Reserved.</i></p>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - May 2002 Progress Report</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">May 2002 Progress Report</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="index">
<dt><a href="#intro">Introduction</a></dt>
<dt><a href="#features">New Features</a></dt>
<dl>
<dt><a href="#aix_shared">Shared Library Support for AIX</a><dd>
<dt><a href="#class_enhancements">Class Enhancements</a><dd>
<dl>
<dt><a href="#operators">Operators</a><dd>
<dt><a href="#iterators">Iterators</a><dd>
<dt><a href="#properties">Properties</a><dd>
<dt><a href="#setattr">setattr</a><dd>
<dt><a href="#module">__module__ Attribute</a><dd>
</dl>
<dt><a href="#back_reference">back_reference</a><dd>
</dl>
<dt><a href="#documentation">Documentation</a></dt>
<dt><a href="#misc">Miscellaneous</a></dt>
<dl class="index">
<dt><a href="#converters">Converters</a></dt>
<dt><a href="#checkins">Checkins Mailing List</a></dt>
<dt><a href="#shared">Shared Libraries</a></dt>
</dl>
<dt><a href="#next">What's Next</a></dt>
</dl>
<h2><a name="intro">Introduction</a></h2>
Aside from library development, work on Boost.Python in May was
focused on reducing the support burden. In recent weeks, responding to
requests for support, espcially surrounding building the library, had
begun to impede progress on development. There was a major push to
release a stable 1.28.0 of Boost, including documentation of <a
href="../../../../tools/build/index.html">Boost.Build</a> and specific
<a href="../building.html">instructions</a> for building Boost.Python
v1. The documentation for Boost.Python v2 was also updated as
described <a href="#documentation">here</a>.
<h2><a name="features">New Features</a></h2>
<h3><a name="aix_shared">Shared Library Support for AIX</a></h3>
The Kull group required the ability to build and test Boost.Python
extensions on AIX, a platform with &quot;creatively designed&quot;
shared library semantics. Making this work was a multi-pronged
effort, involving changes to Boost.Build and some great research by
Martin Casado which uncovered the key mechanism required to allow
shared libraries to use functions from the Python executable. The
current solution used in Boost.Build relies on a <a
href="../../../../tools/build/gen_aix_import_file.py">Python
Script</a> as part of the build process. This is not a problem for
Boost.Python, as Python will be available. However, the commands
issued by the script are so simple that a 100%-pure-Boost.Jam
solution is surely possible. Linking on AIX is sufficiently
interesting to have skewed the Boost.Python development schedule a
bit.
<h3><a name="class_enhancements">Class Enhancements</a></h3>
<h4><a name="operators">Operators</a></h4>
Support for exposing C++ operators and functions as the corresponding
Python special methods was added. Thinking that the Boost.Python
<a href="../special.html#numeric">v1 interface</a> was a little too
esoteric (especially the use of
<code>left_operand&lt;...&gt;/right_operand&lt;...&gt;</code> for
asymmetric operands), I introduced a simple form of <a
href="http://osl.iu.edu/~tveldhui/papers/Expression-Templates/exprtmpl.html">expression
templates</a> which allow users to simply write the expressions that
should be wrapped, as in this <a href="operators.html#examples">example</a>.
<h4><a name="iterators">Iterators</a></h4>
Python iterator support as required by the Kull project resulted in a
highly flexible interface allowing:
<dl>
<dt>Direct exposure of a class' <code>begin()</code> and
<code>end()</code> functions:
<pre>
...
.def(&quot;__iter__&quot;, iterator&lt;list_int&gt;())
</pre>
<dd>
<dt>Creation of iterators from member functions...
<pre>
...
.def(&quot;__iter__&quot;
, range(&amp;my_class::x_begin, &amp;my_class::x_end))
)
</pre>
<dd>
<dt>...and member data:
<pre>
...
.def(&quot;__iter__&quot;
, range(&amp;std::pair&lt;char*,char*&gt;::first, &amp;std::pair&lt;char*,char*&gt;::second))
)
</pre>
<dd>
<dt>The ability to specify <a
href="CallPolicies.html">CallPolicies</a>, e.g. to prevent copying of
heavyweight values:
<pre>
...
.def(&quot;__iter__&quot;,
, range&lt;return_value_policy&lt;copy_non_const_reference&gt; &gt;(
&amp;my_sequence&lt;heavy&gt;::begin
, &amp;my_sequence&lt;heavy&gt;::end))
</pre>
<dd>
</dl>
<h4><a name="properties">Properties</a></h4>
The Kull iteration interfaces also required the ability to iterate
over a sequence specified by an instance's attribute:
<pre>
&gt;&gt;&gt; f = field()
&gt;&gt;&gt; for e in f.elements:
... print e,
</pre>
This forced the exposure of the <a
href="http://www.python.org/2.2/descrintro.html#property"><code>property</code></a>
interface used internally to implement the data member exposure
facility described in <a
href="Mar2002#data_members">March</a>. Properties are an
incredibly useful idiom, so it's good to be able to provide them
at little new development cost.
<h4><a name="setattr">setattr</a></h4>
<code>class_&lt;&gt;</code> acquired a <code>setattr</code> member
function which allows users to easily add new Python objects as class
attributes.
<h4><a name="module">__module__ Attribute</a></h4>
Ralf Grosse-Kunstleve has been working on pickling support for v2. To
make it work correctly, he had to make sure that a class'
<code>__module__</code> attribute was set correctly.
<h3><a name="back_reference"><code>back_reference</code></a></h3>
The new <code>back_reference&lt;T&gt;</code> template can be used as a
function parameter when the user needs access to both a <code>T</code>
argument and to the Python object which manages it. The function will
only match in the overload resolution process if it would match the
same function signature with <code>T</code> substituted for
<code>back_reference&lt;T&gt;</code>. This feature is not yet
documented.
<h2><a name="documentation">Documentation</a></h2>
In a major effort to prepare Boost.Python v2 to replace v1, many pages
of new reference documentation were added:
<blockquote>
<dl>
<dt><a href="CallPolicies.html">CallPolicies.html</a><dd>
<dt><a href="Dereferenceable.html">Dereferenceable.html</a><dd>
<dt><a href="Extractor.html">Extractor.html</a><dd>
<dt><a href="HolderGenerator.html">HolderGenerator.html</a><dd>
<dt><a href="ResultConverter.html">ResultConverter.html</a><dd>
<dt><a href="call_method.html">call_method.html</a><dd>
<dt><a href="callbacks.html">callbacks.html</a><dd>
<dt><a href="data_members.html">data_members.html</a><dd>
<dt><a href="has_back_reference.html">has_back_reference.html</a><dd>
<dt><a href="implicit.html">implicit.html</a><dd>
<dt><a href="instance_holder.html">instance_holder.html</a><dd>
<dt><a href="operators.html">operators.html</a><dd>
<dt><a href="ptr.html">ptr.html</a><dd>
<dt><a href="type_id.html">type_id.html</a><dd>
<dt><a href="with_custodian_and_ward.html">with_custodian_and_ward.html</a><dd>
</dl>
</blockquote>
Major updates were made to the following pages:
<blockquote>
<dl>
<dt><a href="call.html">call.html</a><dd> <dt><a href="updated">updated</a><dd>
<dt><a href="class.html">class.html</a><dd>
<dt><a href="reference.html">reference.html</a><dd>
</dl>
</blockquote>
As usual, careful documentation forces one to consider the
interface again, and there were many interface changes
associated with this effort, including the elevation of the
following components from implementation detail to
first-class library citizen:
<blockquote>
<dl>
<dt>type_id.hpp<dd>
<dt>pointee.hpp<dd>
<dt>lvalue_from_pytype.hpp<dd></dl>
</dl>
</blockquote>
<h2><a name="misc">Miscellaneous</a></h2>
<h3><a name="converters">Converters</a></h3>
It appears that the world of C++ &lt;==&gt; Python conversion rules is
an endlessly-rich area of exploration. Completing the conversions for
<code>char</code> and <code>char const*</code> types, as described at
the end of <a href="Apr2002.html#missing">April's report</a>,
uncovered some interesting new shades to the problem. It turns out to
be worth distinguishing mutable and immutable lvalue conversions,
because despite the fact that Python doesn't understand
<code>const</code>, it does understand immutability (c.f. Python
strings, which expose an immutable <code>char</code> pointer). It is
also worth recognizing types which represent lvalue <i>sequences</i>,
to prevent Python <code>&quot;foobar&quot;</code> from being silently
truncated to C++ <code>'f'</code>. More details on this insight can be
found in the mailing list <a
href="http://mail.python.org/pipermail/c++-sig/2002-May/001023.html">
archive</a>. I don't plan to do anything about this immediately, but I
do think it's the right direction to go in the long run.
<h3><a name="checkins">Checkins Mailing List</a></h3>
In order to better coordinate changes made by multiple developers, I
enabled <a
href="http://sourceforge.net/docman/display_doc.php?docid=772&group_id=1">syncmail</a>
for the Boost.Python CVS trees, and established an associated <a
href="http://lists.sourceforge.net/lists/listinfo/boost-python-cvs">mailing
list</a>. Subscribe to this list to receive notices of each new
checkin.
<h3><a name="shared">Shared Libraries</a></h3>
Beyond the vagaries of dynamic linking on AIX, I have been
participating in a more-general discussion of dynamic linking for
C++. Needless to say, C++ dynamic linking is of critical importance to
Boost.Python: all extension modules are normally built as shared
libraries, and Boost.Python extension modules share a common library
as well.
In fact, there are at least two separate conversations. One
in the C++ standard extensions mailing list concerns what can be
standardized for C++ and shared libraries; the other, mostly on the <a
href="http://gcc.gnu.org/ml/gcc/">gcc</a> mailing list, concerns the
behavior of GCC on Posix/ELF platforms.
Some of the GCC threads are here:
<blockquote>
<a
href="http://gcc.gnu.org/ml/gcc/2002-05/msg02002.html">http://gcc.gnu.org/ml/gcc/2002-05/msg02002.html</a><br>
<a
href="http://gcc.gnu.org/ml/gcc/2002-05/msg02945.html">http://gcc.gnu.org/ml/gcc/2002-05/msg02945.html</a><br>
<a href="http://gcc.gnu.org/ml/gcc/2002-05/msg01758.html">http://gcc.gnu.org/ml/gcc/2002-05/msg01758.html</a>
</blockquote>
<h2><a name="next">What's Next</a></h2>
Development is focused on what's needed to be able to retire
Boost.Python v1. At the moment, that means deciding the user-friendly
interfaces for to_/from_python conversion, and formally exposing the
Python object smart pointers and object wrapper classes. Quite a few
questions have also been showing up recently about how to embed Python
with Boost.Python, and how to link with it statically; the solutions
to these issues will probably have to be formalized before long.
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
11 June, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a>
2002. All Rights Reserved.</i></p>
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - ObjectWrapper Concept</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">ObjectWrapper and TypeWrapper Concepts</h2>
</td>
</tr>
</table>
<hr>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#concept-requirements">Concept Requirements</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#ObjectWrapper-concept">ObjectWrapper Concept</a></dt>
<dt><a href="#TypeWrapper-concept">TypeWrapper Concept</a></dt>
</dl>
</dd>
<dt><a href="#caveat">Caveat</a></dt>
</dl>
<h2><a name="introduction"></a>Introduction</h2>
<p>This page defines two concepts used to describe classes which manage a
Python objects, and which are intended to support usage with a
Python-like syntax.</p>
<h2><a name="concept-requirements"></a>Concept Requirements</h2>
<h3><a name="ObjectWrapper-concept"></a>ObjectWrapper Concept</h3>
Models of the ObjectWrapper concept have <a href=
"object.html#object-spec">object</a> as a publicly-accessible base class,
and are used to supply special construction behavior and/or additional
convenient functionality through (often templated) member functions.
Except when the return type <code>R</code> is itself an <a href=
"#TypeWrapper-concept">TypeWrapper</a>, a member function invocation of
the form
<pre>
x.<i>some_function</i>(<i>a<small>1</small>, a<small>2</small>,...a<small>n</small></i>)
</pre>
always has semantics equivalent to:
<pre>
<a href=
"extract.html#extract-spec">extract</a>&lt;R&gt;(x.attr("<i>some_function</i>")(<a
href=
"object.html#object-spec-ctors">object</a>(<i>a<small>1</small></i>), <a
href=
"object.html#object-spec-ctors">object</a>(<i>a<small>2</small></i>),...<a
href="object.html#object-spec-ctors">object</a>(<i>a<small>n</small></i>)))()
</pre>
When the <code>R</code> is an <a href=
"#TypeWrapper-concept">TypeWrapper</a>, the result type may be
constructed by taking direct posession of:
<pre>
x.attr("<i>some_function</i>")(<a href=
"object.html#object-spec-ctors">object</a>(<i>a<small>1</small></i>), <a
href=
"object.html#object-spec-ctors">object</a>(<i>a<small>2</small></i>),...<a
href=
"object.html#object-spec-ctors">object</a>(<i>a<small>n</small></i>)).ptr()
</pre>
[see <a href="#caveat">caveat</a> below]
<h3><a name="TypeWrapper-concept"></a>TypeWrapper Concept</h3>
TypeWrapper is a refinement of ObjectWrapper which is associated with a
particular Python type <code>X</code>. For a given TypeWrapper
<code>T</code>, a valid constructor expression
<pre>
T(<i>a<small>1</small>, a<small>2</small>,...a<small>n</small></i>)
</pre>
builds a new <code>T</code> object managing the result of invoking
<code>X</code> with arguments corresponding to
<pre>
<a href=
"object.html#object-spec-ctors">object</a>(<i>a<small>1</small></i>), <a
href=
"object.html#object-spec-ctors">object</a>(<i>a<small>2</small></i>),...<a
href=
"object.html#object-spec-ctors">object</a>(<i>a<small>n</small></i>)
</pre>
When used as arguments to wrapped C++ functions, or as the template
parameter to <code><a
href="extract.html#extract-spec">extract</a>&lt;&gt;</code>, only
instances of the associated Python type will be considered a match.
<h3><a name="caveat">Caveat</a></h3>
The upshot of the special member function invocation rules when the
return type is a TypeWrapper is that it is possible for the returned
object to manage a Python object of an inappropriate type. This is not
usually a serious problem; the worst-case result is that errors will be
detected at runtime a little later than they might otherwise be. For an
example of how this can occur, note that the <code><a href=
"dict.html#dict-spec">dict</a></code> member function <code>items</code>
returns an object of type <code><a href=
"list.html#list-spec">list</a></code>. Now suppose the user defines this
<code>dict</code> subclass in Python:
<pre>
&gt;&gt;&gt; class mydict(dict):
... def items(self):
... return tuple(dict.items(self)) # return a tuple
</pre>
Since an instance of <code>mydict</code> is also an instance of
<code>dict</code>, when used as an argument to a wrapped C++ function,
<code><a href="dict.html#dict-spec">boost::python::dict</a></code> can
accept objects of Python type <code>mydict</code>. Invoking
<code>items()</code> on this object can result in an instance of <code><a
href="list.html#list-spec">boost::python::list</a></code> which actually
holds a Python tuple. Subsequent attempts to use list methods (e.g.
<code>append</code>, or any other mutating operation) on this object will
raise the same exception that would occur if you tried to do it from
Python.
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
30 Sept, 2002 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
<p>Permission to copy, use, modify, sell and distribute this software is
granted provided this copyright notice appears in all copies. This
software is provided "as is" without express or implied warranty, and
with no claim as to its suitability for any purpose.</p>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../../../boost.css">
<title>Boost.Python - ResultConverter Concept</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">ResultConverter Concept</h2>
</td>
</tr>
</table>
<hr>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#concept-requirements">Concept Requirements</a></dt>
<dl class="page-index">
<dt><a href="#ResultConverter-concept">ResultConverter Concept</a></dt>
<dt><a href="#ResultConverterGenerator-concept">ResultConverterGenerator Concept</a></dt>
</dl>
</dl>
<h2><a name="introduction"></a>Introduction</h2>
<p>A ResultConverter for a type <code>T</code> is a type whose
instances can be used to convert C++ return values of type
<code>T</code> <code>to_python</code>. A ResultConverterGenerator is
an MPL unary metafunction class which, given the return type of a C++
function, returns a ResultConverter for that type. ResultConverters in
Boost.Python generally inspect library's registry of converters to
find a suitable converter, but converters which don't use the registry
are also possible.
<h2><a name="concept-requirements"></a>Concept Requirements</h2>
<h3><a name="ResultConverter-concept"></a>ResultConverter Concept</h3>
<p>In the table below, <code><b>C</b></code> denotes a ResultConverter
type for a type <b><code>R</code></b> , <code><b>c</b></code> denotes
an object of type <code><b>C</b></code> , and <code><b>r</b></code>
denotes an object of type <code><b>R</b></code>.
<table summary="ResultConverter expressions" border="1" cellpadding="5">
<tr>
<td><b>Expression</b></td>
<td><b>Type</b></td>
<td><b>Semantics</b></td>
</tr>
<tr>
<td valign="top"><code>C c;</code></td>
<td>
<td>Constructs a <code>C</code> object.
</tr>
<tr>
<td valign="top"><code>c.convertible()</code></td>
<td>convertible to <code>bool</code></td>
<td><code>false</code> iff no conversion from any <code>R</code> value
to a Python object is possible.</td>
</tr>
<tr>
<td valign="top"><code>c(r)</code></td>
<td>convertible to <code>PyObject*</code></td>
<td>A pointer to a Python object corresponding to <code>r</code>,
or <code>0</code> iff <code>r</code> could not be converted
<code>to_python</code>, in which case <a
href="http://www.python.org/doc/current/api/exceptionHandling.html#l2h-71">PyErr_Occurred</a>
should return non-zero.</td>
</tr>
</table>
<h3><a name="ResultConverterGenerator-concept"></a>ResultConverterGenerator Concept</h3>
<p>In the table below, <code><b>G</b></code> denotes a
ResultConverterGenerator type and <code><b>R</b></code> denotes a possible
C++ function return type.
<table summary="ResultConverterGenerator expressions" border="1" cellpadding="5">
<tr>
<td><b>Expression</b></td>
<td><b>Requirements</b></td>
</tr>
<tr>
<td valign="top"><code>G::apply&lt;R&gt;::type</code></td>
<td>A ResultConverter type for <code>R</code>.</td>
</table>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
09 May, 2002 <!--Luann's birthday! -->
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>
<p>Permission to copy, use, modify, sell
and distribute this software is granted provided this copyright notice appears
in all copies. This software is provided "as is" without express or implied
warranty, and with no claim as to its suitability for any purpose.
</body>
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - Acknowledgments</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Acknowledgments</h2>
</td>
</tr>
</table>
<hr>
<p><a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a> is
the architect, designer, and implementor of <b>Boost.Python</b>.</p>
<p>Joel de Guzman implemented the <a href="overloads.html">default
argument support</a> and wrote the excellent tutorial documentation.</p>
<p><a href="../../../../people/ralf_w_grosse_kunstleve.htm">Ralf W.
Grosse-Kunstleve</a> implemented the <a href="pickle.html">pickle
support</a>, and has enthusiastically supported the library since its
birth, contributing to design decisions and providing invaluable
real-world insight into user requirements. Ralf has written some
extensions for converting C++ containers that I hope will be incorporated
into the library soon. He also implemented the cross-module support in
the first version of Boost.Python. More importantly, Ralf makes sure
nobody forgets the near-perfect synergy of C++ and Python for solving the
problems of large-scale software construction.</p>
<p><a href="mailto:achim@procoders.net">Achim Domma</a> contributed some
of the <a href="reference.html#object_wrappers">Object Wrappers</a> and
HTML templates for this documentation. Dave Hawkes contributed
inspiration for the use of the <code><a href=
"scope.html#scope-spec">scope</a></code> class to simplify module
definition syntax. Pearu Pearson wrote some of the test cases that are in
the current test suite.</p>
<p>Martin Casado solved some sticky problems which allow us to build the
Boost.Python shared library for AIX's crazy dynamic linking model.</p>
<p>The development of this version of Boost.Python was funded in part by
the <a href="http://www.llnl.gov/">Lawrence Livermore National
Laboratories</a> and by the <a href="http://cci.lbl.gov/">Computational
Crystallography Initiative</a> at Lawrence Berkeley National
Laboratories.</p>
<p><a href="http://kogs-www.informatik.uni-hamburg.de/~koethe/">Ullrich
Koethe</a> provided the implementation of inheritance and special
method/operator support in the first version of Boost.Python.</p>
<p>The first version of Boost.Python would not have been possible without
the support of Dragon Systems, which supported its development and
release as a Boost library.</p>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
08 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;boost/python/args.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/args.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#keyword-expression"><i>keyword-expressions</i></a></dt>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><code><a href=
"#args-spec">args</a>(</code>...<code>)</code></dt>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>Supplies a family of overloaded functions for specifying argument
keywords for wrapped C++ functions.</p>
<h2><a name="keyword-expression"></a><i>keyword-expressions</i></h2>
<p>A <b>keyword-expression</b> results in an object which holds a
sequence of <a href="definitions.html#ntbs">ntbs</a>es, and whose type
encodes the number of keywords specified.</p>
<h2><a name="functions"></a>Functions</h2>
<h3><a name="args-spec"></a><code>args(</code>...<code>)</code></h3>
<pre>
<i>unspecified1</i> args(char const*);
<i>unspecified2</i> args(char const*, char const*);
.
.
.
<i>unspecifiedN</i> args(char const*, char const*, ... char const*);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> Every argument must be a <a href=
"definitions.html#ntbs">ntbs</a>.</dt>
<dt><b>Returns:</b> an object representing a <a href=
"#keyword-expression"><i>keyword-expression</i></a> encapsulating the
arguments passed.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<pre>
#include &lt;boost/python/def.hpp&gt;
using namespace boost::python;
int f(int x, int y, int z);
BOOST_PYTHON_MODULE(xxx)
{
def("f", f, args("x", "y", "z"));
}
</pre>
<p>Revised 05 November, 2001</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - Bibliography</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Bibliography</h2>
</td>
</tr>
</table>
<hr>
{{bibliographical information}}
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
05 November, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a>
2002. All Rights Reserved.</i></p>
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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;call.hpp&gt;</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;call.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#functions">Functions</a></dt>
<dl class="page-index">
<dt><a href="#call-spec">call</a></dt>
</dl>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>
<code>&lt;boost/python/call.hpp&gt;</code> defines the <a
href="#call-spec"><code>call</code></a> family of overloaded function
templates, used to invoke Python callable objects from C++.
<h2><a name="functions"></a>Functions</h2>
<pre>
<a name="call-spec">template &lt;class R, class A1, class A2, ... class A<i>n</i>&gt;</a>
R call(PyObject* callable, A1 const&amp;, A2 const&amp;, ... A<i>n</i> const&amp;)
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>R</code> is a pointer type, reference
type, or a complete type with an accessible copy constructor</dt>
<dt><b>Effects:</b> Invokes <code>callable(a1,&nbsp;a2,&nbsp;...a<i>n</i>)</code> in
Python, where <code>a1</code>...<code>a<i>n</i></code> are the arguments to
<code>call()</code>, converted to Python objects.
<dt><b>Returns:</b> The result of the Python call, converted to the C++ type <code>R</code>.</dt>
</dt>
<dt><b>Rationale:</b> For a complete semantic description and
rationale, see <a href="callbacks.html">this page</a>.
</dt>
</dl>
<h2><a name="examples"></a>Example(s)</h2>
The following C++ function applies a Python callable object to its two
arguments and returns the result. If a Python exception is raised or
the result can't be converted to a <code>double</code>, an exception
is thrown.
<pre>
double apply2(PyObject* func, double x, double y)
{
return boost::python::call&lt;double&gt;(func, x, y);
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
9 May, 2002 <!-- Luann's birthday! -->
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a>
2002. All Rights Reserved.</i></p>
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<head>
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<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;call_method.hpp&gt;</h2>
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<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#call_method-spec">call_method</a></dt>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/call_method.hpp&gt;</code> defines the <a href=
"#call_method-spec"><code>call_method</code></a> family of overloaded
function templates, used to invoke callable attributes of Python objects
from C++.</p>
<h2><a name="functions"></a>Functions</h2>
<pre>
<a name=
"call_method-spec">template &lt;class R, class A1, class A2, ... class A<i>n</i>&gt;</a>
R call_method(PyObject* self, char const* method, A1 const&amp;, A2 const&amp;, ... A<i>n</i> const&amp;)
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>R</code> is a pointer type, reference type,
or a complete type with an accessible copy constructor</dt>
<dt><b>Effects:</b> Invokes
<code>self.<i>method</i>(a1,&nbsp;a2,&nbsp;...a<i>n</i>)</code> in
Python, where <code>a1</code>...<code>a<i>n</i></code> are the
arguments to <code>call_method()</code>, converted to Python objects.
For a complete semantic description, see <a href="callbacks.html">this
page</a>.</dt>
<dt><b>Returns:</b> The result of the Python call, converted to the C++
type <code>R</code>.</dt>
<dt><b>Rationale:</b> <code>call_method</code> is critical to
implementing C++ virtual functions which are overridable in Python, as
shown by the example below.</dt>
</dl>
<h2><a name="examples"></a>Example(s)</h2>
The following C++ illustrates the use of <code>call_method</code> in
wrapping a class with a virtual function that can be overridden in
Python:
<h3>C++ Module Definition</h3>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/utility.hpp&gt;
#include &lt;cstring&gt;
// class to be wrapped
class Base
{
public:
virtual char const* class_name() const { return "Base"; }
virtual ~Base();
};
bool is_base(Base* b)
{
return !std::strcmp(b-&gt;class_name(), "Base");
}
// Wrapper code begins here
using namespace boost::python;
// Callback class
class Base_callback : public Base
{
public:
Base_callback(PyObject* self) : m_self(self) {}
char const* class_name() const { return <b>call_method</b>(m_self, "class_name"); }
char const* Base_name() const { return Base::class_name(); }
private:
PyObject* const m_self;
};
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
def("is_base", is_base);
class_&lt;Base,Base_callback, noncopyable&gt;("Base")
.def("class_name", &amp;Base_callback::Base_name)
;
}
</pre>
<h3>Python Code</h3>
<pre>
&gt;&gt;&gt; from my_module import *
&gt;&gt;&gt; class Derived(Base):
... def __init__(self):
... Base.__init__(self)
... def class_name(self):
... return self.__class__.__name__
...
&gt;&gt;&gt; is_base(Base()) # calls the class_name() method from C++
1
&gt;&gt;&gt; is_base(Derived())
0
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
28 Sept, 2002 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
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<h1 align="center">Boost.Python</h1>
<h2 align="center">Calling Python Functions and Methods</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#argument_handling">Argument Handling</a></dt>
<dt><a href="#result_handling">Result Handling</a></dt>
<dt><a href="#result_handling">Rationale</a></dt>
</dl>
<hr>
<h2><a name="introduction">Introduction</a></h2>
The simplest way to call a Python function from C++, given an <code><a
href="object.html#object-spec">object</a></code> instance <code>f</code>
holding the function, is simply to invoke its function call operator.
<pre>
f("tea", 4, 2) // In Python: f('tea', 4, 2)
</pre>
And of course, a method of an <code><a href=
"object.html#object-spec">object</a></code> instance <code>x</code> can
be invoked by using the function-call operator of the corresponding
attribute:
<pre>
x.attr("tea")(4, 2); // In Python: x.tea(4, 2)
</pre>
<p>If you don't have an <code>object</code> instance, Boost.Python
provides two families of function templates, <code><a href=
"call.html#call-spec">call</a></code> and <code><a href=
"call_method.html#call_method-spec">call_method</a></code>, for invoking
Python functions and methods respectively on <code>PyObject*</code>s. The
interface for calling a Python function object (or any Python callable
object) looks like:</p>
<pre>
call&lt;ResultType&gt;(callable_object, a1, a2... a<i>N</i>);
</pre>
Calling a method of a Python object is similarly easy:
<pre>
call_method&lt;ResultType&gt;(self_object, "<i>method-name</i>", a1, a2... a<i>N</i>);
</pre>
This comparitively low-level interface is the one you'll use when
implementing C++ virtual functions that can be overridden in Python.
<h2><a name="argument_handling">Argument Handling</a></h2>
<p>Arguments are converted to Python according to their type. By default,
the arguments <code>a1</code>...<code>a<i>N</i></code> are copied into
new Python objects, but this behavior can be overridden by the use of
<code><a href="ptr.html#ptr-spec">ptr()</a></code> and <a href=
"../../../bind/ref.html#reference_wrapper">ref()</a>:</p>
<pre>
class X : boost::noncopyable
{
...
};
void apply(PyObject* callable, X&amp; x)
{
// Invoke callable, passing a Python object which holds a reference to x
boost::python::call&lt;void&gt;(callable, boost::ref(x));
}
</pre>
In the table below, <code><b>x</b></code> denotes the actual argument
object and <code><b>cv</b></code> denotes an optional
<i>cv-qualification</i>: "<code>const</code>", "<code>volatile</code>",
or "<code>const volatile</code>".
<table border="1" summary="class_ template parameters">
<tr>
<th>Argument Type</th>
<th>Behavior</th>
</tr>
<tr>
<td><code>T cv&amp;</code><br>
<code>T cv</code></td>
<td>The Python argument is created by the same means used for the
return value of a wrapped C++ function returning <code>T</code>. When
<code>T</code> is a class type, that normally means <code>*x</code>
is copy-constructed into the new Python object.</td>
</tr>
<tr>
<td><code>T*</code></td>
<td>If <code>x&nbsp;==&nbsp;0</code>, the Python argument will be
<code><a href=
"http://www.python.org/doc/current/lib/bltin-null-object.html">None</a></code>.
Otherwise, the Python argument is created by the same means used for
the return value of a wrapped C++ function returning <code>T</code>.
When <code>T</code> is a class type, that normally means
<code>*x</code> is copy-constructed into the new Python object.</td>
</tr>
<tr>
<td><code><a href=
"../../../bind/ref.html#reference_wrapper">boost::reference_wrapper</a>&lt;T&gt;</code></td>
<td>The Python argument contains a pointer to, rather than a copy of,
<code>x.get()</code>. Note: failure to ensure that no Python code
holds a reference to the resulting object beyond the lifetime of
<code>*x.get()</code> <b>may result in a crash!</b></td>
</tr>
<tr>
<td><code><a href=
"ptr.html#pointer_wrapper-spec">pointer_wrapper</a>&lt;T&gt;</code></td>
<td>If <code>x.get()&nbsp;==&nbsp;0</code>, the Python argument will
be <code><a href=
"http://www.python.org/doc/current/lib/bltin-null-object.html">None</a></code>.
Otherwise, the Python argument contains a pointer to, rather than a
copy of, <code>*x.get()</code>. Note: failure to ensure that no
Python code holds a reference to the resulting object beyond the
lifetime of <code>*x.get()</code> <b>may result in a crash!</b></td>
</tr>
</table>
<h2><a name="result_handling">Result Handling</a></h2>
In general, <code>call&lt;ResultType&gt;()</code> and
<code>call_method&lt;ResultType&gt;()</code> return
<code>ResultType</code> by exploiting all lvalue and rvalue
<code>from_python</code> converters registered for ResultType and
returning a copy of the result. However, when <code>ResultType</code> is
a pointer or reference type, Boost.Python searches only for lvalue
converters. To prevent dangling pointers and references, an exception
will be thrown if the Python result object has only a single reference
count.
<h2><a name="rationale">Rationale</a></h2>
In general, to get Python arguments corresponding to
<code>a1</code>...<code>a<i>N</i></code>, a new Python object must be
created for each one; should the C++ object be copied into that Python
object, or should the Python object simply hold a reference/pointer to
the C++ object? In general, the latter approach is unsafe, since the
called function may store a reference to the Python object somewhere. If
the Python object is used after the C++ object is destroyed, we'll crash
Python.
<p>In keeping with the philosophy that users on the Python side shouldn't
have to worry about crashing the interpreter, the default behavior is to
copy the C++ object, and to allow a non-copying behavior only if the user
writes <code><a href="../../../bind/ref.html">boost::ref</a>(a1)</code>
instead of a1 directly. At least this way, the user doesn't get dangerous
behavior "by accident". It's also worth noting that the non-copying
("by-reference") behavior is in general only available for class types,
and will fail at runtime with a Python exception if used otherwise[<a
href="#1">1</a>].</p>
<p>However, pointer types present a problem: one approach is to refuse to
compile if any aN has pointer type: after all, a user can always pass
<code>*aN</code> to pass "by-value" or <code>ref(*aN)</code> to indicate
a pass-by-reference behavior. However, this creates a problem for the
expected null pointer to <code>None</code> conversion: it's illegal to
dereference a null pointer value.</p>
<p>The compromise I've settled on is this:</p>
<ol>
<li>The default behavior is pass-by-value. If you pass a non-null
pointer, the pointee is copied into a new Python object; otherwise the
corresponding Python argument will be None.</li>
<li>if you want by-reference behavior, use <code>ptr(aN)</code> if
<code>aN</code> is a pointer and <code>ref(aN)</code> otherwise. If a
null pointer is passed to <code>ptr(aN)</code>, the corresponding
Python argument will be <code>None</code>.</li>
</ol>
<p>As for results, we have a similar problem: if <code>ResultType</code>
is allowed to be a pointer or reference type, the lifetime of the object
it refers to is probably being managed by a Python object. When that
Python object is destroyed, our pointer dangles. The problem is
particularly bad when the <code>ResultType</code> is char const* - the
corresponding Python String object is typically uniquely-referenced,
meaning that the pointer dangles as soon as <code>call&lt;char
const*&gt;(...)</code> returns.</p>
<p>The old Boost.Python v1 deals with this issue by refusing to compile
any uses of <code>call&lt;char const*&gt;()</code>, but this goes both
too far and not far enough. It goes too far because there are cases where
the owning Python string object survives beyond the call (just for
instance, when it's the name of a Python class), and it goes not far
enough because we might just as well have the same problem with a
returned pointer or reference of any other type.</p>
<p>In Boost.Python v2 this is dealt with by:</p>
<ol>
<li>lifting the compile-time restriction on const char* callback
returns</li>
<li>detecting the case when the reference count on the result Python
object is 1 and throwing an exception inside of
<code>call&lt;U&gt;(...)</code> when <code>U</code> is a pointer or
reference type.</li>
</ol>
This should be acceptably safe because users have to explicitly specify a
pointer/reference for <code>U</code> in <code>call&lt;U&gt;</code>, and
they will be protected against dangles at runtime, at least long enough
to get out of the <code>call&lt;U&gt;(...)</code> invocation.
<hr>
<a name="1">[1]</a> It would be possible to make it fail at compile-time
for non-class types such as int and char, but I'm not sure it's a good
idea to impose this restriction yet.
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
17 April, 2002 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

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Here's the plan:
I aim to provide an interface similar to that of Boost.Python v1's
callback<>::call(...) for dealing with callbacks. The interface will
look like:
returning<ResultType>::call("method_name", self_object, a1, a2...);
or
returning<ResultType>::call(callable_object, a1, a2...);
ARGUMENT HANDLING
There is an issue concerning how to make Python objects from the
arguments a1...aN. A new Python object must be created; should the C++
object be copied into that Python object, or should the Python object
simply hold a reference/pointer to the C++ object? In general, the
latter approach is unsafe, since the called function may store a
reference to the Python object somewhere. If the Python object is used
after the C++ object is destroyed, we'll crash Python.
I plan to make the copying behavior the default, and to allow a
non-copying behavior if the user writes boost::ref(a1) instead of a1
directly. At least this way, the user doesn't get dangerous behavior "by
accident". It's also worth noting that the non-copying ("by-reference")
behavior is in general only available for class types, and will fail at
runtime with a Python exception if used otherwise**
However, pointer types present a problem: My first thought is to refuse
to compile if any aN has pointer type: after all, a user can always pass
*aN to pass "by-value" or ref(*aN) to indicate a pass-by-reference
behavior. However, this creates a problem for the expected NULL pointer
=> None conversion: it's illegal to dereference a null pointer value.
We could use another construct, say "ptr(aN)", to deal with null
pointers, but then what does it mean? We know what it does when aN is
NULL, but it might either have by-value or by-reference behavior when aN
is non-null.
The compromise I've settled on is this:
1. The default behavior is pass-by-value. If you pass a non-null
pointer, the pointee is copied into a new Python object; otherwise
the corresponding Python argument will be None.
2. if you want by-reference behavior, use ptr(aN) if aN is a pointer
and ref(aN) otherwise. If a null pointer is passed to ptr(aN), the
corresponding Python argument will be None.
RESULT HANDLING
As for results, we have a similar problem: if ResultType is allowed to
be a pointer or reference type, the lifetime of the object it refers to
is probably being managed by a Python object. When that Python object is
destroyed, our pointer dangles. The problem is particularly bad when the
ResultType is char const* - the corresponding Python String object is
typically uniquely-referenced, meaning that the pointer dangles as soon
as returning<char const*>::call() returns.
Boost.Python v1 deals with this issue by refusing to compile any uses of
callback<char const*>::call(), but IMO this goes both too far and not
far enough. It goes too far because there are cases where the owning
String object survives beyond the call (just for instance when it's the
name of a Python class), and it goes not far enough because we might
just as well have the same problem with any returned pointer or
reference.
I propose to address this in Boost.Python v2 by
1. lifting the compile-time restriction on const
char* callback returns
2. detecting the case when the reference count on the
result Python object is 1 and throwing an exception
inside of returning<U>::call() when U is a pointer or
reference type.
I think this is acceptably safe because users have to explicitly specify
a pointer/reference for U in returning<U>, and they will be protected
against dangles at runtime, at least long enough to get out of the
returning<U>::call() invocation.
-Dave
**It would be possible to make it fail at compile-time for non-class
types such as int and char, but I'm not sure it's a good idea to impose
this restriction yet.

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<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Headers &lt;boost/python/class.hpp&gt;,
&lt;boost/python/class_fwd.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#class_-spec">Class template
<code>class_</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#class_-spec-synopsis">Class <code>class_</code>
synopsis</a></dt>
<dt><a href="#class_-spec-ctors">Class <code>class_</code>
constructors</a></dt>
<dt><a href="#class_-spec-modifiers">Class <code>class_</code>
modifier functions</a></dt>
</dl>
</dd>
<dt><a href="#bases-spec">Class template
<code>bases</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#bases-spec-synopsis">Class template
<code>bases</code> synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/class.hpp&gt;</code> defines the interface
through which users expose their C++ classes to Python. It declares the
<code>class_</code> class template, which is parameterized on the class
type being exposed. It also exposes the <code>init</code>,
<code>optional</code> and <code>bases</code> utility class templates,
which are used in conjunction with <code>class_</code>.</p>
<p><code>&lt;boost/python/class_fwd.hpp&gt;</code> contains a forward
declaration of the <code>class_</code> class template.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="class_-spec"></a>Class template
<code>class_&lt;T,&nbsp;<font color="#007F00">Bases,&nbsp;HeldType,
NonCopyable</font>&gt;</code></h3>
<p>Creates a Python class associated with the C++ type passed as its
first parameter. Although it has four template parameters, only the first
one is required. The three optional arguments can actually be supplied
<font color="#007F00"><b>in any order</b></font>; Boost.Python determines
the role of the argument from its type.<br>
<br>
</p>
<table border="1" summary="class_ template parameters">
<tr>
<th>Template Parameter</th>
<th>Requirements</th>
<th>Semantics</th>
<th>Default</th>
</tr>
<tr>
<td><code>T</code></td>
<td>A class type.</td>
<td>The class being wrapped</td>
</tr>
<tr>
<td><code><font color="#007F00">Bases</font></code></td>
<td>A specialization of <a href=
"#bases-spec"><code>bases&lt;</code>...<code>&gt;</code></a> which
specifies previously-exposed C++ base classes of <code>T</code><a
href="#footnote_1">[1]</a>.</td>
<td>Registers <code>from_python</code> conversions from wrapped
<code>T</code> instances to each of its exposed direct and indirect
bases. For each polymorphic base <code>B</code>, registers
conversions from indirectly-held wrapped <code>B</code> instances to
<code>T</code>.</td>
<td><code><a href="#bases">bases&lt;&gt;</a></code></td>
</tr>
<tr>
<td><code><font color="#007F00">HeldType</font></code></td>
<td>Must be <code>T</code>, a class derived from <code>T</code>, or a
<a href="Dereferenceable.html">Dereferenceable</a> type for which
<code><a href=
"pointee.html#pointee-spec">pointee</a>&lt;HeldType&gt;::type</code>
is <code>T</code> or a class derived from <code>T</code>.</td>
<td>Specifies the type which is actually embedded in a Python object
wrapping a <code>T</code> instance. More details <a href=
"#HeldType">below</a>.</td>
<td><code>T</code></td>
</tr>
<tr>
<td><code><font color="#007F00">NonCopyable</font></code></td>
<td>If supplied, must be <a href=
"../../../utility/utility.htm#Class%20noncopyable">boost::noncopyable</a>.</td>
<td>Suppresses automatic registration of <code>to_python</code>
conversions which copy <code>T</code> instances. Required when
<code>T</code> has no publicly-accessible copy constructor.</td>
<td>An unspecified type other than
<code>boost::noncopyable</code>.</td>
</tr>
</table>
<h4><a name="#HeldType">HeldType Semantics</a></h4>
<ol>
<li>If <code>HeldType</code> is derived from T, its exposed
constructor(s) must accept an initial <code>PyObject*</code> argument
which refers back to the Python object that contains the
<code>HeldType</code> instance, as shown in <a href=
"call_method.html#example">this example</a>. This argument is not
included in the <em><a href=
"init.html#init-expressions">init-expression</a></em> passed to <a
href="#class-spec-modifiers"><code>def(init_expr)</code></a>, below,
nor is it passed explicitly by users when Python instances of
<code>T</code> are created. This idiom allows C++ virtual functions
which will be overridden in Python to access the Python object so the
Python method can be invoked. Boost.Python automatically registers
additional converters which allow wrapped instances of <code>T</code>
to be passed to wrapped C++ functions expecting <code>HeldType</code>
arguments.</li>
<li>Because Boost.Python will always allow wrapped instances of
<code>T</code> to be passed in place of <code>HeldType</code>
arguments, specifying a smart pointer for <code>HeldType</code> allows
users to pass Python <code>T</code> instances where a smart
pointer-to-<code>T</code> is expected. Smart pointers such as
<code>std::auto_ptr&lt;&gt;</code> or <code><a href=
"../../../smart_ptr/shared_ptr.htm">boost::shared_ptr&lt;&gt;</a></code>
which contain a nested type <code>element_type</code> designating the
referent type are automatically supported; additional smart pointer
types can be supported by specializing <a href=
"pointee.html#pointee-spec">pointee&lt;HeldType&gt;</a>.</li>
<li>As in case 1 above, when <code>HeldType</code> is a smart pointer
to a class derived from <code>T</code>, the initial
<code>PyObject*</code> argument must be supplied by all of
<code>HeldType</code>'s exposed constructors.</li>
<li>Except in cases 1 and 3, users may optionally specify that T itself
gets initialized with a similar initial <code>PyObject*</code> argument
by specializing <a href=
"has_back_reference.html#has_back_reference-spec">has_back_reference&lt;T&gt;</a>.</li>
</ol>
<h4><a name="class_-spec-synopsis"></a>Class template <code>class_</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class T
<font color="#007F00"> , class Bases = bases&lt;&gt;
, class HeldType = T
, class NonCopyable = <i>unspecified</i>
&gt;
</font> class class_ : public <a href="object.html#object-spec">object</a>
{
// Constructors with default __init__
class_(char const* name);
class_(char const* name, char const* docstring);
// Constructors, specifying non-default __init__
template &lt;class Init&gt;
class_(char const* name, Init);
template &lt;class Init&gt;
class_(char const* name, char const* docstring, Init);
// Exposing additional __init__ functions
template &lt;class Init&gt;
class_&amp; def(Init);
// defining methods
template &lt;class F&gt;
class_&amp; def(char const* name, F f);
template &lt;class Fn, class A1&gt;
class_&amp; def(char const* name, Fn fn, A1 const&amp;);
template &lt;class Fn, class A1, class A2&gt;
class_&amp; def(char const* name, Fn fn, A1 const&amp;, A2 const&amp;);
template &lt;class Fn, class A1, class A2, class A3&gt;
class_&amp; def(char const* name, Fn fn, A1 const&amp;, A2 const&amp;, A3 const&amp;);
// exposing operators
template &lt;<i>unspecified</i>&gt;
class_&amp; def(<a href=
"operators.html#operator_-spec">detail::operator_</a>&lt;unspecified&gt;);
// Raw attribute modification
template &lt;class U&gt;
class_&amp; setattr(char const* name, U const&amp;);
// exposing data members
template &lt;class D&gt;
class_&amp; def_readonly(char const* name, D T::*pm);
template &lt;class D&gt;
class_&amp; def_readwrite(char const* name, D T::*pm);
// property creation
template &lt;class Get&gt;
void add_property(char const* name, Get const&amp; fget);
template &lt;class Get, class Set&gt;
void add_property(char const* name, Get const&amp; fget, Set const&amp; fset);
// pickle support
template &lt;typename PickleSuite&gt;
self&amp; def_pickle(PickleSuite const&amp;);
};
}}
</pre>
<h4><a name="class_-spec-ctors"></a>Class template <code>class_</code>
constructors</h4>
<pre>
class_(char const* name);
class_(char const* name, char const* docstring);
template &lt;class Init&gt;
class_(char const* name, Init init_spec);
template &lt;class Init&gt;
class_(char const* name, char const* docstring, Init init_spec);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>. If <code>docstring</code> is supplied, it must be an
<a href="definitions.html#ntbs">ntbs</a>. If <code>init_spec</code> is
supplied, it must be either the special enumeration constant
<code>no_init</code> or an <a href=
"init.html#init-expression">init-expression</a> compatible with
<code>T</code>.</dt>
<dt><b>Effects:</b> Constructs a <code>class_</code> object holding a
Boost.Python extension class named <code>name</code>. The
<code>name</code>d attribute of the <a href=
"scope.html#introduction">current scope</a> is bound to the new
extension class.</dt>
<dd>
<ul>
<li>If supplied, the value of <code>docstring</code> is bound to
the <code>__doc__</code> attribute of the extension class.</li>
<li>If <code>init_spec</code> is <code>no_init</code>, a special
<code>__init__</code> function is generated which always raises a
Python exception. Otherwise, <code>this-&gt;def(init_spec)</code>
is called.</li>
<li>If <code>init_spec</code> is not supplied,
<code>this-&gt;def(init&lt;&gt;())</code> is called.</li>
</ul>
</dd>
<dt><b>Rationale:</b>Allowing the user to specify constructor arguments
in the <code>class_&lt;&gt;</code> constructor helps her to avoid the
common run-time errors which result from invoking wrapped member
functions without having exposed an <code>__init__</code> function
which creates the requisite <code>T</code> instance. Types which are
not default-constructible will cause a compile-time error unless
<code>Init</code> is supplied. The user must always supply
<code>name</code> as there is currently no portable method to derive
the text of the class name from its type.</dt>
</dl>
<h4><a name="class_-spec-modifiers"></a>Class template
<code>class_</code> modifier functions</h4>
<pre>
template &lt;class Init&gt;
class_&amp; def(Init init_expr);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>init_expr</code> is the result of an <a
href="init.html#init-expression">init-expression</a> compatible with
<code>T</code>.</dt>
<dt><b>Effects:</b> For each <a href="init.html#init-expressions">valid
prefix</a> <em>P</em> of <code>Init</code>, adds an
<code>__init__(</code>...<code>)</code> function overload to the
extension class accepting <em>P</em> as arguments. Each overload
generated constructs an object of <code>HeldType</code> according to
the semantics described <a href="#HeldType">above</a>, using a copy of
<code>init_expr</code>'s <a href="CallPolicies.html">call policies</a>.
If the longest <a href="init.html#init-expressions">valid prefix</a> of <code>Init</code> contains <em>N</em>
types and <code>init_expr</code> holds <em>M</em> keywords, an initial
sequence of the keywords are used for all but the first
<em>N</em>&nbsp;-&nbsp;<em>M</em> arguments of each overload.</dt>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Allows users to easily expose a class'
constructor to Python.</dt>
</dl>
<br>
<pre>
template &lt;class F&gt;
class_&amp; def(char const* name, Fn fn);
template &lt;class Fn, class A1&gt;
class_&amp; def(char const* name, Fn fn, A1 const&amp; a1);
template &lt;class Fn, class A1, class A2&gt;
class_&amp; def(char const* name, Fn fn, A1 const&amp; a1, A2 const&amp; a2);
template &lt;class Fn, class A1, class A2, class A3&gt;
class_&amp; def(char const* name, Fn fn, A1 const&amp; a1, A2 const&amp; a2, A3 const&amp; a3);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.</dt>
<dd>
<ul>
<li>
If <code>a1</code> is the result of an <a href=
"overloads.html#overload-dispatch-expression"><em>overload-dispatch-expression</em></a>,
only the second form is allowed and fn must be a pointer
to function or pointer to member function whose <a
href="definitions.html#arity">arity</a> is the same as A1's <a href=
"overloads.html#overload-dispatch-expression"><em>maximum arity</em></a>.
<dl>
<dt><b>Effects:</b> For each prefix <em>P</em> of
<code>Fn</code>'s sequence of argument types, beginning
with the one whose length is <code>A1</code>'s <a href=
"overloads.html#overload-dispatch-expression"><em>minimum
arity</em></a>, adds a
<code><em>name</em>(</code>...<code>)</code> method
overload to the extension class. Each overload generated
invokes
<code>a1</code>'s call-expression with <em>P</em>, using a copy
of <code>a1</code>'s <a href="CallPolicies.html">call
policies</a>. If the longest valid prefix of <code>A1</code>
contains <em>N</em> types and <code>a1</code> holds <em>M</em>
keywords, an initial sequence of the keywords are used for all
but the first <em>N</em>&nbsp;-&nbsp;<em>M</em> arguments of
each overload.<br>
</dt>
</dl>
</li>
<li>
Otherwise, a single method overload is built around fn, which
must not be null:
<ul>
<li>If fn is a function pointer, its first argument must be of
the form <code>U</code>, <code>U&nbsp;<em>cv</em>&amp;</code>,
<code>U&nbsp;<em>cv</em>*</code>, or
<code>U&nbsp;<em>cv</em>*&nbsp;const&amp;</code>, where
<code>T*</code> is convertible to <code>U*</code>, and
<code>a1</code>-<code>a3</code>, if supplied, may be selected
in any order from the table below.</li>
<li>Otherwise, if fn is a member function pointer, its target
must be <code>T</code> or one of its public base classes, and
<code>a1</code>-<code>a3</code>, if supplied, may be selected
in any order from the table below.</li>
<li>Otherwise, <code>Fn</code> must be [derived from] <code><a
href="object.html#object-spec">object</a></code>, and
<code>a1-a2</code>, if supplied, may be selcted in any order
from the first two rows of the table below. To be useful,
<code>fn</code> should be <a href=
"http://www.python.org/doc/current/lib/built-in-funcs.html#l2h-6">
callable</a>.</li>
</ul>
<table border="1" summary="def() optional arguments">
<tr>
<th>Memnonic Name</th>
<th>Requirements/Type properties</th>
<th>Effects</th>
</tr>
<tr>
<td>docstring</td>
<td>Any <a href="definitions.html#ntbs">ntbs</a>.</td>
<td>Value will be bound to the <code>__doc__</code> attribute
of the resulting method overload.</td>
</tr>
<tr>
<td>policies</td>
<td>A model of <a href=
"CallPolicies.html">CallPolicies</a></td>
<td>A copy will be used as the call policies of the resulting
method overload.</td>
</tr>
<tr>
<td>keywords</td>
<td>The result of a <a href=
"args.html#keyword-expression"><em>keyword-expression</em></a>
specifying no more arguments than the <a href=
"definitions.html#arity">arity</a> of <code>fn</code>.</td>
<td>A copy will be used as the call policies of the resulting
method overload.</td>
</tr>
</table>
</li>
</ul>
</dd>
<dt><b>Returns:</b> <code>*this</code></dt>
</dl>
<pre>
template &lt;<i>unspecified</i>&gt;
class_&amp; def(<a href=
"operators.html#operator_-spec">detail::operator_</a>&lt;unspecified&gt;);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> Adds a Python <a href=
"http://www.python.org/doc/ref/specialnames.html">special method</a> as
described <a href="operators.html">here</a>.</dt>
<dt><b>Returns:</b> <code>*this</code></dt>
</dl>
<pre>
template &lt;class U&gt;
class_&amp; setattr(char const* name, U const&amp; u);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.</dt>
<dt><b>Effects:</b> Converts u to Python and adds it to the attribute
dictionary of the extension class:</dt>
<dd>
<blockquote>
<code><a href=
"http://www.python.org/doc/current/api/object.html#l2h-166">PyObject_SetAttrString</a>(this-&gt;ptr(),&nbsp;name,&nbsp;<a
href="object.html#object-spec-ctors">object</a>(u).ptr());</code>
</blockquote>
</dd>
<dt><b>Returns:</b> <code>*this</code></dt>
</dl>
<br>
<pre>
template &lt;class Get&gt;
void add_property(char const* name, Get const&amp; fget);
template &lt;class Get, class Set&gt;
void add_property(char const* name, Get const&amp; fget, Set const&amp; fset);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.</dt>
<dt><b>Effects:</b> Creates a new Python <a href=
"http://www.python.org/current/descrintro.html#property"><code>property</code></a>
class instance, passing <code><a href=
"object.html#object-spec-ctors">object</a>(fget)</code> (and <code><a
href="object.html#object-spec-ctors">object</a>(fset)</code> in the
second form) to its constructor, then adds that property to the Python
class object under construction with the given attribute
<code>name</code>.</dt>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Allows users to easily expose functions that can
be invoked from Python with attribute access syntax.</dt>
</dl>
<br>
<pre>
template &lt;class D&gt;
class_&amp; def_readonly(char const* name, D T::*pm);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.</dt>
<dt><b>Effects:</b></dt>
<dd>
<pre>
this-&gt;add_property(name, <a href=
"data_members.html#make_getter-spec">make_getter</a>(pm));
</pre>
</dd>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Allows users to easily expose a class' data
member such that it can be inspected from Python with a natural
syntax.</dt>
</dl>
<pre>
template &lt;class D&gt;
class_&amp; def_readwrite(char const* name, D T::*pm);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b></dt>
<dd>
<pre>
this-&gt;add_property(name, <a href=
"data_members.html#make_getter-spec">make_getter</a>(pm), <a href=
"data_members.html#make_setter-spec">make_setter</a>(pm));
</pre>
</dd>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Allows users to easily expose a class' data
member such that it can be inspected and set from Python with a natural
syntax.</dt>
</dl>
<pre>
template &lt;typename PickleSuite&gt;
class_&amp; def_pickle(PickleSuite const&amp;);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> PickleSuite must be publically derived from
<a href="pickle.html"
><code>pickle_suite</code></a>.</dt>
<dt><b>Effects:</b> Defines a legal combination of the special
attributes and methods:
<code>__getinitargs__</code>,
<code>__getstate__</code>,
<code>__setstate__</code>,
<code>__getstate_manages_dict__</code>,
<code>__safe_for_unpickling__</code>,
<code>__reduce__</code>
</dt>
<dt><b>Returns:</b> <code>*this</code></dt>
<dt><b>Rationale:</b> Provides an
<a href="pickle.html"
>easy to use high-level interface</a>
for establishing complete pickle support for the wrapped class.
The user is protected by compile-time consistency checks.</dt>
</dl>
<br>
<h3><a name="bases-spec"></a>Class template
<code>bases&lt;T1,&nbsp;T2,</code>...<code>TN&gt;</code></h3>
<p>An <a href="../../../mpl/doc/ref/Sequences.html">MPL sequence</a>
which can be used in <code>class_&lt;</code>...<code>&gt;</code>
instantiations indicate a list of base classes.</p>
<h4><a name="bases-spec-synopsis"></a>Class template <code>bases</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;T1 = <i>unspecified</i>,...T<i>n</i> = <i>unspecified</i>&gt;
struct bases
{};
}}
</pre>
<h2><a name="examples"></a>Example(s)</h2>
<p>Given a C++ class declaration:</p>
<pre>
class Foo : public Bar, public Baz
{
public:
Foo(int x, char const* y);
Foo(double);
std::string const&amp; name() { return m_name; }
void name(char const*);
double value; // public data
private:
...
};
</pre>
A corresponding Boost.Python extension class can be created with:
<pre>
using namespace boost::python;
class_&lt;Foo,bases&lt;Bar,Baz&gt; &gt;("Foo",
"This is Foo's docstring."
"It describes our Foo extension class",
init&lt;int,char const*&gt;(args("x","y"), "__init__ docstring")
)
.def(init&lt;double&gt;())
.def("get_name", &amp;Foo::get_name, return_internal_reference&lt;&gt;())
.def("set_name", &amp;Foo::set_name)
.def_readwrite("value", &amp;Foo::value)
;
</pre>
<hr>
<a name="footnote_1">[1]</a> By "previously-exposed" we mean that the for
each <code>B</code> in <code>bases</code>, an instance of
<code>class_&lt;B<font color="#007F00">, ...</font>&gt;</code> must have
already been constructed.
<pre>
class_&lt;Base&gt;("Base");
class_&lt;Derived, bases&lt;Base&gt; &gt;("Derived");
</pre>
Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 Sept, 2002 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

View File

@@ -1,141 +0,0 @@
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - Configuration</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Configuration</h2>
</td>
</tr>
</table>
<hr>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#app-defined">Application Defined Macros</a></dt>
<dt><a href="#lib-defined-impl">Library Defined Implementation
Macros</a></dt>
</dl>
<h2><a name="introduction"></a>Introduction</h2>
<p><b>Boost.Python</b> uses several configuration macros in <a href=
"http://www.boost.org/libs/config/config.htm">&lt;boost/config.hpp&gt;</a>,
as well as configuration macros meant to be supplied by the application.
These macros are documented here.</p>
<h2><a name="app-defined"></a>Application Defined Macros</h2>
<p>These are the macros that may be defined by an application using
<b>Boost.Python</b>. Note that if you extend a strict interpretation of the C++
standard to cover dynamic libraries, using different values of these
macros when compiling different libraries (including extension modules
and the <b>Boost.Python</b> library itself) is a violation of the <a href=
"definitions.html#ODR">ODR</a>. However, we know of no C++
implementations on which this particular violation is detectable or
causes any problems.</p>
<table summary="application defined macros" width="100%" cellpadding=
"10">
<tr>
<th align="left"><b>Macro</b></td>
<th><b>Default</b></td>
<th align="left"><b>Meaning</b></td>
</tr>
<tr>
<td valign="top"><code>BOOST_PYTHON_MAX_ARITY</code></td>
<td valign="top" align="center">15</td>
<td valign="top">The maximum <a href="definitions.html#arity">arity</a> of any
function, member function, or constructor to be wrapped, invocation
of a <b>Boost.Python</b> function wich is specified as taking arguments
<code>x1,&nbsp;x2,</code>...<code>X</code><i>n</i>. This includes, in
particular, callback mechanisms such as <code><a href=
"object.html#object-spec">object</a>::operator()(</code>...<code>)</code>
or <code><a href=
"call_method.html#call_method-spec">call_method</a>&lt;R&gt;(</code>...<code>
)</code>.</td>
</tr>
<tr>
<td valign="top"><code>BOOST_PYTHON_MAX_BASES</code></td>
<td valign="top" align="center">10</td>
<td valign="top">The maximum number of template arguments to the <code><a href=
"class.html#bases-spec">bases</a>&lt;</code>...<code>&gt;</code>
class template, which is used to specify the bases of a wrapped C++
class..</td>
</tr>
</table>
<h2><a name="lib-defined-impl"></a>Library Defined Implementation
Macros</h2>
<p>These macros are defined by <b>Boost.Python</b> and are
implementation details of interest only to implementors and those porting
to new platforms.</p>
<table summary="library defined implementation macros" width="100%"
cellpadding="10">
<tr>
<th align="left"><b>Macro</b></td>
<th><b>Default</b></td>
<th align="left"><b>Meaning</b></td>
</tr>
<tr>
<td valign="top"><code>BOOST_PYTHON_TYPE_ID_NAME</code></td>
<td valign="top" align="center"><i>not&nbsp;defined</i></td>
<td valign="top">If defined, this indicates that the type_info comparison across
shared library boundaries does not work on this platform. In other
words, if shared-lib-1 passes <code>typeid(T)</code> to a function in
shared-lib-2 which compares it to <code>typeid(T)</code>, that
comparison may return <code>false</code>. If this macro is #defined,
Boost.Python uses and compares <code>typeid(T).name()</code> instead
of using and comparing the <code>std::type_info</code> objects
directly.</td>
</tr>
</table>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
04 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

View File

@@ -1,147 +0,0 @@
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python -
&lt;boost/python/copy_const_reference.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/copy_const_reference.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#copy_const_reference-spec">Class
<code>copy_const_reference</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#copy_const_reference-spec-synopsis">Class
<code>copy_const_reference</code> synopsis</a></dt>
<dt><a href="#copy_const_reference-spec-metafunctions">Class
<code>copy_const_reference</code> metafunctions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="copy_const_reference-spec"></a>Class
<code>copy_const_reference</code></h3>
<p><code>copy_const_reference</code> is a model of <a href=
"ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a>
which can be used to wrap C++ functions returning a reference-to-const
type such that the referenced value is copied into a new Python
object.</p>
<h4><a name="copy_const_reference-spec-synopsis"></a>Class
<code>copy_const_reference</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
struct copy_const_reference
{
template &lt;class T&gt; struct apply;
};
}}
</pre>
<h4><a name="copy_const_reference-spec-metafunctions"></a>Class
<code>copy_const_reference</code> metafunctions</h4>
<pre>
template &lt;class T&gt; struct apply
</pre>
<dl class="metafunction-semantics">
<dt><b>Requires:</b> <code>T</code> is <code>U const&amp;</code> for
some <code>U</code>.</dt>
<dt><b>Returns:</b> <code>typedef <a href=
"to_python_value.html#to_python_value-spec">to_python_value</a>&lt;T&gt;
type;</code></dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<h3>C++ Module Definition</h3>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/copy_const_reference.hpp&gt;
#include &lt;boost/python/return_value_policy.hpp&gt;
// classes to wrap
struct Bar { int x; }
struct Foo {
Foo(int x) : { b.x = x; }
Bar const&amp; get_bar() const { return b; }
private:
Bar b;
};
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
class_&lt;Bar&gt;("Bar");
class_&lt;Foo&gt;("Foo", init&lt;int&gt;())
.def("get_bar", &amp;Foo::get_bar
, return_value_policy&lt;copy_const_reference&gt;())
;
}
</pre>
<h3>Python Code</h3>
<pre>
&gt;&gt;&gt; from my_module import *
&gt;&gt;&gt; f = Foo(3) # create a Foo object
&gt;&gt;&gt; b = f.get_bar() # make a copy of the internal Bar object
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

View File

@@ -1,147 +0,0 @@
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<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python -
&lt;boost/python/copy_non_const_reference.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/copy_non_const_reference.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#copy_non_const_reference-spec">Class
<code>copy_non_const_reference</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#copy_non_const_reference-spec-synopsis">Class
<code>copy_non_const_reference</code> synopsis</a></dt>
<dt><a href=
"#copy_non_const_reference-spec-metafunctions">Class
<code>copy_non_const_reference</code> metafunctions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="copy_non_const_reference-spec"></a>Class
<code>copy_non_const_reference</code></h3>
<p><code>copy_non_const_reference</code> is a model of <a href=
"ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a>
which can be used to wrap C++ functions returning a
reference-to-non-const type such that the referenced value is copied into
a new Python object.</p>
<h4><a name="copy_non_const_reference-spec-synopsis"></a>Class
<code>copy_non_const_reference</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
struct copy_non_const_reference
{
template &lt;class T&gt; struct apply;
};
}}
</pre>
<h4><a name="copy_non_const_reference-spec-metafunctions"></a>Class
<code>copy_non_const_reference</code> metafunctions</h4>
<pre>
template &lt;class T&gt; struct apply
</pre>
<dl class="metafunction-semantics">
<dt><b>Requires:</b> <code>T</code> is <code>U&amp;</code> for some
non-const <code>U</code>.</dt>
<dt><b>Returns:</b> <code>typedef <a href=
"to_python_value.html#to_python_value-spec">to_python_value</a>&lt;T&gt;
type;</code></dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<p>C++ code:</p>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/copy_non_const_reference.hpp&gt;
#include &lt;boost/python/return_value_policy.hpp&gt;
// classes to wrap
struct Bar { int x; }
struct Foo {
Foo(int x) : { b.x = x; }
Bar&amp; get_bar() { return b; }
private:
Bar b;
};
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
class_&lt;Bar&gt;("Bar");
class_&lt;Foo&gt;("Foo", init&lt;int&gt;())
.def("get_bar", &amp;Foo::get_bar
, return_value_policy&lt;copy_non_const_reference&gt;())
;
}
</pre>
Python Code:
<pre>
&gt;&gt;&gt; from my_module import *
&gt;&gt;&gt; f = Foo(3) # create a Foo object
&gt;&gt;&gt; b = f.get_bar() # make a copy of the internal Bar object
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September, 2001
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

View File

@@ -1,159 +0,0 @@
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN">
<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;boost/python/data_members.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/data_members.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#make_getter-spec">make_getter</a></dt>
<dt><a href="#make_setter-spec">make_setter</a></dt>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code><a href="#make_getter-spec">make_getter</a>()</code> and
<code><a href="#make_setter-spec">make_setter</a>()</code> are the
functions used internally by <code>class_&lt;&gt;::<a href=
"class.html#class_-spec-modifiers">def_readonly</a></code> and
<code>class_&lt;&gt;::<a href=
"class.html#class_-spec-modifiers">def_readwrite</a></code> to produce
Python callable objects which wrap C++ data members.</p>
<h2><a name="functions"></a>Functions</h2>
<pre>
<a name="make_getter-spec">template &lt;class C, class D&gt;</a>
<a href="object.html#object-spec">object</a> make_getter(D C::*pm);
template &lt;class C, class D, class Policies&gt;
<a href=
"object.html#object-spec">object</a> make_getter(D C::*pm, Policies const&amp; policies);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>Policies</code> is a model of <a href=
"CallPolicies.html">CallPolicies</a>.</dt>
<dt><b>Effects:</b> Creates a Python callable object which accepts a
single argument that can be converted <code>from_python</code> to
<code>C*</code>, and returns the corresponding member <code>D</code>
member of the <code>C</code> object, converted <code>to_python</code>.
If <code>policies</code> is supplied, it will be applied to the
function as described <a href="CallPolicies.html">here</a>.</dt>
<dt><b>Returns:</b> An instance of <a href=
"object.html#object-spec">object</a> which holds the new Python
callable object.</dt>
</dl>
<pre>
<a name="make_setter-spec">template &lt;class C, class D&gt;</a>
<a href="object.html#object-spec">object</a> make_setter(D C::*pm);
template &lt;class C, class D, class Policies&gt;
<a href=
"object.html#object-spec">object</a> make_setter(D C::*pm, Policies const&amp; policies);
</pre>
<dl class="function*-semantics">
<dt><b>Requires:</b> <code>Policies</code> is a model of <a href=
"CallPolicies.html">CallPolicies</a>.</dt>
<dt><b>Effects:</b> Creates a Python callable object which, when called
from Python, expects two arguments which can be converted
<code>from_python</code> to <code>C*</code> and
<code>D&nbsp;const&amp;</code>, respectively, and sets the
corresponding <code>D</code> member of the <code>C</code> object. If
<code>policies</code> is supplied, it will be applied to the function
as described <a href="CallPolicies.html">here</a>.</dt>
<dt><b>Returns:</b> An instance of <a href=
"object.html#object-spec">object</a> which holds the new Python
callable object.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<p>The code below uses make_getter and make_setter to expose a data
member as functions:</p>
<pre>
#include &lt;boost/python/data_members.hpp&gt;
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
struct X
{
X(int x) : y(x) {}
int y;
};
using namespace boost::python;
BOOST_PYTHON_MODULE_INIT(data_members_example)
{
class_&lt;X&gt;("X", init&lt;int&gt;())
.def("get", make_getter(&amp;X::y))
.def("set", make_setter(&amp;X::y))
;
}
</pre>
It can be used this way in Python:
<pre>
&gt;&gt;&gt; from data_members_example import *
&gt;&gt;&gt; x = X(1)
&gt;&gt;&gt; x.get()
1
&gt;&gt;&gt; x.set(2)
&gt;&gt;&gt; x.get()
2
</pre>
<p>
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

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<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;boost/python/def.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/def.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#def-spec">def</a></dt>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code><a href="#def-spec">def</a>()</code> is the function which can
be used to expose C++ functions and callable objects as Python functions
in the current <code><a href="scope.html">scope</a></code>.</p>
<h2><a name="functions"></a>Functions</h2>
<a name="def-spec"></a>def
<pre>
template &lt;class F&gt;
void def(char const* name, F f);
template &lt;class Fn, class A1&gt;
void def(char const* name, Fn fn, A1 const&amp;);
template &lt;class Fn, class A1, class A2&gt;
void def(char const* name, Fn fn, A1 const&amp;, A2 const&amp;);
template &lt;class Fn, class A1, class A2, class A3&gt;
void def(char const* name, Fn fn, A1 const&amp;, A2 const&amp;, A3 const&amp;);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.</dt>
<dd>
<ul>
<li>
If <code>a1</code> is the result of an <a href=
"overloads.html#overload-dispatch-expression"><em>overload-dispatch-expression</em></a>,
only the second form is allowed and fn must be a pointer to
function or pointer to member function whose <a href=
"definitions.html#arity">arity</a> is the same as A1's <a href=
"overloads.html#overload-dispatch-expression"><em>maximum
arity</em></a>.
<dl>
<dt><b>Effects:</b> For each prefix <em>P</em> of
<code>Fn</code>'s sequence of argument types, beginning with
the one whose length is <code>A1</code>'s <a href=
"overloads.html#overload-dispatch-expression"><em>minimum
arity</em></a>, adds a
<code><em>name</em>(</code>...<code>)</code> function overload
to the <a href="scope.html">current scope</a>. Each overload
generated invokes <code>a1</code>'s call-expression with
<em>P</em>, using a copy of <code>a1</code>'s <a href=
"CallPolicies.html">call policies</a>. If the longest valid
prefix of <code>A1</code> contains <em>N</em> types and
<code>a1</code> holds <em>M</em> keywords, an initial sequence
of the keywords are used for all but the first
<em>N</em>&nbsp;-&nbsp;<em>M</em> arguments of each
overload.<br>
</dt>
</dl>
</li>
<li>
Otherwise, a single function overload built around fn (which must
not be null) is added to the <a href="scope.html">current
scope</a>:
<ul>
<li>If fn is a function or member function pointer,
<code>a1</code>-<code>a3</code> (if supplied) may be selected
in any order from the table below.</li>
<li>Otherwise, <code>Fn</code> must be [derived from] <code><a
href="object.html#object-spec">object</a></code>, and
<code>a1-a2</code> (if supplied) may be selcted in any order
from the first two rows of the table below. To be useful,
<code>fn</code> should be <a href=
"http://www.python.org/doc/current/lib/built-in-funcs.html#l2h-6">
callable</a>.</li>
</ul>
<table border="1" summary="def() optional arguments">
<tr>
<th>Memnonic Name</th>
<th>Requirements/Type properties</th>
<th>Effects</th>
</tr>
<tr>
<td>docstring</td>
<td>Any <a href="definitions.html#ntbs">ntbs</a>.</td>
<td>Value will be bound to the <code>__doc__</code> attribute
of the resulting method overload.</td>
</tr>
<tr>
<td>policies</td>
<td>A model of <a href=
"CallPolicies.html">CallPolicies</a></td>
<td>A copy will be used as the call policies of the resulting
method overload.</td>
</tr>
<tr>
<td>keywords</td>
<td>The result of a <a href=
"args.html#keyword-expression"><em>keyword-expression</em></a>
specifying no more arguments than the <a href=
"definitions.html#arity">arity</a> of <code>fn</code>.</td>
<td>A copy will be used as the call policies of the resulting
method overload.</td>
</tr>
</table>
</li>
</ul>
</dd>
</dl>
<h2><a name="examples"></a>Example</h2>
<pre>
#include &lt;boost/python/def.hpp&gt;
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/args.hpp&gt;
char const* foo(int x, int y) { return "foo"; }
BOOST_PYTHON_MODULE(def_test)
{
def("foo", foo, args("x", "y"), "foo's docstring");
}
</pre>
<p>
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
03 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

View File

@@ -1,170 +0,0 @@
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<meta name="generator" content="HTML Tidy, see www.w3.org">
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<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python -
&lt;boost/python/default_call_policies.hpp&gt;</title>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/default_call_policies.hpp&gt;</h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#classes">Classes</a>
<dd>
<dl class="page-index">
<dt><a href="#default_call_policies-spec">Class
<code>default_call_policies</code></a>
<dd>
<dl class="page-index">
<dt><a href="#default_call_policies-spec-synopsis">Class
<code>default_call_policies</code> synopsis</a>
<dt><a href="#default_call_policies-spec-statics">Class
<code>default_call_policies</code> static functions</a>
</dl>
<dt><a href="#default_result_converter-spec">Class
<code>default_result_converter</code></a>
<dd>
<dl class="page-index">
<dt><a href="#default_result_converter-spec-synopsis">Class
<code>default_result_converter</code> synopsis</a>
<dt><a href="#default_result_converter-spec-metafunctions">Class
<code>default_result_converter</code> metafunctions</a>
</dl>
</dl>
<dt><a href="#examples">Example</a>
</dl>
<hr>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="default_call_policies-spec"></a>Class
<code>default_call_policies</code></h3>
<p><code>default_call_policies</code> is a model of <a href=
"CallPolicies.html">CallPolicies</a> with no <code>precall</code> or
<code>postcall</code> behavior and a <code>result_converter</code> which
handles by-value returns. Wrapped C++ functions and member functions use
<code>default_call_policies</code> unless otherwise specified. You may find
it convenient to derive new models of <a href=
"CallPolicies.html">CallPolicies</a> from
<code>default_call_policies</code>.
<h4><a name="default_call_policies-spec-synopsis"></a>Class
<code>default_call_policies</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
struct default_call_policies
{
static bool precall(PyObject*);
static PyObject* postcall(PyObject*, PyObject* result);
typedef <a href=
"#default_result_converter-spec">default_result_converter</a> result_converter;
};
}}
</pre>
<h4><a name="default_call_policies-spec-statics"></a>Class
<code>default_call_policies</code> static functions</h4>
<pre>
bool precall(PyObject*);
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>true</code>
<dt><b>Throws:</b> nothing
</dl>
<pre>
PyObject* postcall(PyObject*, PyObject* result);
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>result</code>
<dt><b>Throws:</b> nothing
</dl>
<h3><a name="default_result_converter-spec"></a>Class
<code>default_result_converter</code></h3>
<p><code>default_result_converter</code> is a model of <a href=
"ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a> which can be
used to wrap C++ functions returning non-pointer types, <code>char
const*</code>, and <code>PyObject*</code>, by-value.
<h4><a name="default_result_converter-spec-synopsis"></a>Class
<code>default_result_converter</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
struct default_result_converter
{
template &lt;class T&gt; struct apply;
};
}}
</pre>
<h4><a name="default_result_converter-spec-metafunctions"></a>Class
<code>default_result_converter</code> metafunctions</h4>
<pre>
template &lt;class T&gt; struct apply
</pre>
<dl class="metafunction-semantics">
<dt><b>Requires:</b> <code>T</code> is not a reference type. If
<code>T</code> is a pointer type, <code>T</code> is <code>const
char*</code> or <code>PyObject*</code>.
<dt><b>Returns:</b> <code>typedef <a href=
"to_python_value.html#to_python_value-spec">to_python_value</a>&lt;T
const&amp;&gt; type;</code>
</dl>
<h2><a name="examples"></a>Example</h2>
<p>This example comes from the Boost.Python implementation itself. Because
the <a href=
"return_value_policy.html#return_value_policy-spec">return_value_policy</a>
class template does not implement <code>precall</code> or
<code>postcall</code> behavior, its default base class is
<code>default_call_policies</code>:
<pre>
template &lt;class Handler, class Base = default_call_policies&gt;
struct return_value_policy : Base
{
typedef Handler result_converter;
};
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
05 November, 2001
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>

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<title>Boost.Python - Definitions</title>
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</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Definitions</h2>
</td>
</tr>
</table>
<hr>
<dl class="definitions">
<dt><b><a name="arity">arity</a>:</b> The number of arguments accepted
by a function or member function. Unless otherwise specified, the
hidden "<code>this</code>" argument to member functions is not counted
when specifying arity</dt>
<dd><br>
</dd>
<dt><b><a name="ntbs">ntbs</a>:</b> Null-Terminated Byte String, or
`C'-string. C++ string literals are <strong>ntbs</strong>es. An
<strong>ntbs</strong> must never be null.</dt>
<dd><br>
</dd>
<dt><b><a name="raise">raise</a>:</b> Exceptions in Python are
"raised", not "thrown", as they are in C++. When this documentation
says that some Python exception is "raised" in the context of C++ code,
it means that the corresponding Python exception is set via the <a
href=
"http://www.python.org/doc/current/api/exceptionHandling.html">Python/'C'
API</a>, and <code><a href=
"errors.html#throw_error_already_set-spec">throw_error_already_set</a>()</code>
is called.</dt>
<dd><br>
</dd>
<dt><b><a name="POD">POD</a>:</b> A technical term from the C++
standard. Short for "Plain Ol'Data": A POD-struct is an aggregate class
that has no non-static data members of type pointer to member,
non-POD-struct, non-POD-union (or array of such types) or reference,
and has no user-defined copy assign- ment operator and no user-defined
destructor. Similarly, a POD-union is an aggregate union that has no
non-static data members of type pointer to member, non-POD-struct,
non-POD-union (or array of such types) or reference, and has no
user-defined copy assignment operator and no user-defined destructor. A
POD class is a class that is either a POD-struct or a POD-union. An
aggregate is an array or a class (clause 9) with no user-declared
constructors (12.1), no private or protected non-static data members
(clause 11), no base classes (clause 10), and no virtual functions
(10.3).</dt>
<dd><br>
</dd>
<dt><b><a name="ODR">ODR</a>:</b> The &quot;One Definition
Rule&quot;, which says that any entity in a C++ program must have the same definition in all translation units (object files) which make up a program.
</dt>
<dd><br>
</dd>
</dl>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
03 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<title>Boost.Python - &lt;boost/python/dict.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/dict.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#dict-spec">Class <code>dict</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#dict-spec-synopsis">Class <code>dict</code>
synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>Exposes a <a href=
"ObjectWrapper.html#TypeWrapper-concept">TypeWrapper</a> for the Python
<a href=
"http://www.python.org/dev/doc/devel/lib/typesmapping.html">dict</a>
type.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="dict-spec"></a>Class <code>dict</code></h3>
<p>Exposes the <a href=
"http://www.python.org/dev/doc/devel/lib/typesmapping.html">mapping
protocol</a> of Python's built-in <code>dict</code> type. The semantics
of the constructors and member functions defined below can be fully
understood by reading the <a href=
"ObjectWrapper.html#TypeWrapper-concept">TypeWrapper</a> concept
definition. Since <code>dict</code> is publicly derived from <code><a
href="object.html#object-spec">object</a></code>, the public object
interface applies to <code>dict</code> instances as well.</p>
<h4><a name="dict-spec-synopsis"></a>Class <code>dict</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
class dict : public object
{
dict();
template&lt; class T &gt;
dict(T const &amp; data);
// modifiers
void clear();
dict copy();
template &lt;class T1, class T2&gt;
tuple popitem();
template &lt;class T&gt;
object setdefault(T const &amp;k);
template &lt;class T1, class T2&gt;
object setdefault(T1 const &amp; k, T2 const &amp; d);
void update(object_cref E);
template&lt; class T &gt;
void update(T const &amp; E);
// observers
list values() const;
object get(object_cref k) const;
template&lt;class T&gt;
object get(T const &amp; k) const;
object get(object_cref k, object_cref d) const;
object get(T1 const &amp; k, T2 const &amp; d) const;
bool has_key(object_cref k) const;
template&lt; class T &gt;
bool has_key(T const &amp; k) const;
list items() const;
object iteritems() const;
object iterkeys() const;
object itervalues() const;
list keys() const;
};
}}
</pre>
<h2><a name="examples"></a>Example</h2>
<pre>
using namespace boost::python;
dict swap_object_dict(object target, dict d)
{
dict result = extract&lt;dict&gt;(target.attr("__dict__"));
target.attr("__dict__") = d;
return result;
}
</pre>
<p>Revised 30 September, 2002</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<title>Boost.Python - &lt;boost/python/enum.hpp&gt;</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
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<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/enum.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#enum_-spec">Class template
<code>enum_</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#enum_-spec-synopsis">Class template <code>enum_</code>
synopsis</a></dt>
<dt><a href="#enum_-spec-ctors">Class template <code>enum_</code>
constructors</a></dt>
<dt><a href="#enum_-spec-modifiers">Class template <code>enum_</code>
modifier functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/enum.hpp&gt;</code> defines the
interface through which users expose their C++ enumeration types
to Python. It declares the
<code>enum_</code> class template, which is parameterized on the
enumeration type being exposed. </p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="enum_-spec"></a>Class template
<code>enum_&lt;T&gt;</code></h3>
<p>Creates a Python class derived from Python's <code>int</code>
type which is associated with the C++ type passed as its first
parameter.
<h4><a name="enum_-spec-synopsis"></a>Class template <code>enum_</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class T&gt;
class enum_ : public <a href="object.html#object-spec">object</a>
{
enum_(char const* name);
inline enum_&lt;T&gt;&amp; value(char const* name, T);
};
}}
</pre>
<h4><a name="enum_-spec-ctors"></a>Class template <code>enum_</code>
constructors</h4>
<pre>
enum_(char const* name);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.
<dt><b>Effects:</b> Constructs an <code>enum_</code> object
holding a Python extension type derived from <code>int</code>
which is named <code>name</code>. The
<code>name</code>d attribute of the <a href=
"scope.html#introduction">current scope</a> is bound to the new
extension type.</dt>
</dl>
<h4><a name="enum_-spec-modifiers"></a>Class template
<code>enum_</code> modifier functions</h4>
<pre>
inline enum_&lt;T&gt;&amp; value(char const* name, T x);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>name</code> is an <a href=
"definitions.html#ntbs">ntbs</a> which conforms to Python's <a
href=
"http://www.python.org/doc/current/ref/identifiers.html">identifier
naming rules</a>.
<dt><b>Effects:</b> adds an instance of the wrapped enumeration
type with value <code>x</code> to the type's dictionary as the
<code>name</code>d attribute</dt>.
<dt><b>Returns:</b> <code>*this</code></dt>
</dl>
<h2><a name="examples"></a>Example(s)</h2>
<p>C++ module definition
<pre>
#include &lt;boost/python/enum.hpp&gt;
#include &lt;boost/python/def.hpp&gt;
#include &lt;boost/python/module.hpp&gt;
using namespace boost::python;
enum color { red = 1, green = 2, blue = 4 };
color identity_(color x) { return x; }
BOOST_PYTHON_MODULE(enums)
{
enum_&lt;color&gt;(&quot;color&quot;)
.value(&quot;red&quot;, red)
.value(&quot;green&quot;, green)
.value(&quot;blue&quot;, blue)
;
def(&quot;identity&quot;, identity_);
}
</pre>
<p>Interactive Python:
<pre>
&gt;&gt;&gt; from enums import *
&gt;&gt;&gt; identity(color.red)
enums.color.red
&gt;&gt;&gt; identity(color.green)
enums.color.green
&gt;&gt;&gt; identity(color.blue)
enums.color.blue
&gt;&gt;&gt; identity(color(1))
enums.color.red
&gt;&gt;&gt; identity(color(2))
enums.color.green
&gt;&gt;&gt; identity(color(3))
enums.color(3)
&gt;&gt;&gt; identity(color(4))
enums.color.blue
&gt;&gt;&gt; identity(1)
Traceback (most recent call last):
File &quot;&lt;stdin&gt;&quot;, line 1, in ?
TypeError: bad argument type for built-in operation
</pre>
<hr>
Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
03 October, 2002 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
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<html>
<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;boost/python/errors.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/errors.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#error_already_set-spec">Class
<code>error_already_set</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#error_already_set-spec-synopsis">Class
<code>error_already_set</code> synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#handle_exception-spec">handle_exception</a></dt>
<dt><a href="#expect_non_null-spec">expect_non_null</a></dt>
<dt><a href=
"#throw_error_already_set-spec">throw_error_already_set</a></dt>
</dl>
</dd>
<dt><a href="#examples">Examples</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/errors.hpp&gt;</code> provides types and
functions for managing and translating between Python and C++ exceptions.
This is relatively low-level functionality that is mostly used internally
by Boost.Python. Users should seldom need it.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="error_already_set-spec"></a>Class
<code>error_already_set</code></h3>
<p><code>error_already_set</code> is an exception type which can be
thrown to indicate that a Python error has occurred. If thrown, the
precondition is that <a href=
"http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71">PyErr_Occurred()</a>
returns a value convertible to <code>true</code>. Portable code shouldn't
throw this exception type directly, but should instead use <code><a href=
"#throw_error_already_set-spec">throw_error_already_set</a>()</code>,
below.</p>
<h4><a name="error_already_set-spec-synopsis"></a>Class error_already_set
synopsis</h4>
<pre>
namespace boost { namespace python
{
class error_already_set {};
}}
</pre>
<h2><a name="functions"></a>Functions</h2>
<pre>
<a name=
"handle_exception-spec">template &lt;class T&gt; bool handle_exception</a>(T f) throw();
void handle_exception() throw();
</pre>
<dl class="handle_exception-semantics">
<dt><b>Requires:</b> The first form requires that the expression
<code><a href=
"../../../function/doc/reference.html#functionN">function0</a>&lt;void&gt;(f)</code>
is valid. The second form requires that a C++ exception is currently
being handled (see section 15.1 in the C++ standard).</dt>
<dt><b>Effects:</b> The first form calls <code>f()</code> inside a
<code>try</code> block which first attempts to use all registered <a
href="exception_translator.html">exception translators</a>. If none of
those translates the exception, the <code>catch</code> clauses then set
an appropriate Python exception for the C++ exception caught, returning
<code>true</code> if an exception was thrown, <code>false</code>
otherwise. The second form passes a function which rethrows the
exception currently being handled to the first form.</dt>
<dt><b>Postconditions:</b> No exception is being handled</dt>
<dt><b>Throws:</b> nothing</dt>
<dt><b>Rationale:</b> At inter-language boundaries it is important to
ensure that no C++ exceptions escape, since the calling language
usually doesn't have the equipment neccessary to properly unwind the
stack. Use <code>handle_exception</code> to manage exception
translation whenever your C++ code is called directly from the Python
API. This is done for you automatically by the usual function wrapping
facilities: <code><a href=
"make_function.html#make_function-spec">make_function</a>()</code>,
<code><a href=
"make_function.html#make_constructor-spec">make_constructor</a>()</code>,
<code><a href="def.html#def-spec">def</a>()</code> and <code><a href=
"class.html#def-spec">class_::def</a>()</code>. The second form can be
more convenient to use (see the <a href="#examples">example</a> below),
but various compilers have problems when exceptions are rethrown from
within an enclosing <code>try</code> block.</dt>
</dl>
<pre>
<a name=
"expect_non_null-spec">template &lt;class T&gt; T* expect_non_null(T* x);</a>
</pre>
<dl class="expect_non_null-semantics">
<dt><b>Returns:</b> <code>x</code></dt>
<dt><b>Throws:</b> <code><a href=
"#error_already_set-spec">error_already_set</a>()</code> iff <code>x ==
0</code>.</dt>
<dt><b>Rationale:</b> Simplifies error-handling when calling functions
in the <a href="http://www.python.org/doc/2.2/api/api.html">Python/C
API</a> which return 0 on error.</dt>
</dl>
<pre>
<a name="throw_error_already_set-spec">void throw_error_already_set();</a>
</pre>
<dl class="throw_error_already_set-semantics">
<dt><b>Effects:</b> <code>throw&nbsp;<a href=
"#error_already_set-spec">error_already_set</a>();</code></dt>
</dl>
<dl>
<dt><b>Rationale:</b> Many platforms and compilers are not able to
consistently catch exceptions thrown across shared library boundaries.
Using this function from the Boost.Python library ensures that the
appropriate <code>catch</code> block in <code><a href=
"#handle_exception-spec">handle_exception</a>()</code> can catch the
exception.</dt>
</dl>
<h2><a name="examples"></a>Examples</h2>
<pre>
#include &lt;string&gt;
#include &lt;boost/python/errors.hpp&gt;
#include &lt;boost/python/object.hpp&gt;
#include &lt;boost/python/handle.hpp&gt;
// Returns a std::string which has the same value as obj's "__name__"
// attribute.
std::string get_name(boost::python::object obj)
{
// throws if there's no __name__ attribute
PyObject* p = boost::python::expect_non_null(
PyObject_GetAttrString(obj.ptr(), "__name__"));
char const* s = PyString_AsString(p);
if (s != 0)
Py_DECREF(p);
// throws if it's not a Python string
std::string result(
boost::python::expect_non_null(
PyString_AsString(p)));
Py_DECREF(p); // Done with p
return result;
}
//
// Demonstrate form 1 of handle_exception
//
// Place into result a Python Int object whose value is 1 if a and b have
// identical "__name__" attributes, 0 otherwise.
void same_name_impl(PyObject*&amp; result, boost::python::object a, boost::python::object b)
{
result = PyInt_FromLong(
get_name(a) == get_name(a2));
}
object borrowed_object(PyObject* p)
{
return boost::python::object(
boost::python::handle&lt;&gt;(
boost::python::borrowed(a1)));
}
// This is an example Python 'C' API interface function
extern "C" PyObject*
same_name(PyObject* args, PyObject* keywords)
{
PyObject* a1;
PyObject* a2;
PyObject* result = 0;
if (!PyArg_ParseTuple(args, const_cast&lt;char*&gt;("OO"), &amp;a1, &amp;a2))
return 0;
// Use boost::bind to make an object compatible with
// boost::Function0&lt;void&gt;
if (boost::python::handle_exception(
boost::bind&lt;void&gt;(same_name_impl, boost::ref(result), borrowed_object(a1), borrowed_object(a2))))
{
// an exception was thrown; the Python error was set by
// handle_exception()
return 0;
}
return result;
}
//
// Demonstrate form 2 of handle_exception. Not well-supported by all
// compilers.
//
extern "C" PyObject*
same_name2(PyObject* args, PyObject* keywords)
{
PyObject* a1;
PyObject* a2;
PyObject* result = 0;
if (!PyArg_ParseTuple(args, const_cast&lt;char*&gt;("OO"), &amp;a1, &amp;a2))
return 0;
try {
return PyInt_FromLong(
get_name(borrowed_object(a1)) == get_name(borrowed_object(a2)));
}
catch(...)
{
// If an exception was thrown, translate it to Python
boost::python::handle_exception();
return 0;
}
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/exception_translator.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href=
"#register_exception_translator-spec">register_exception_translator</a></dt>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>As described <a href="errors.html#handle_exception-spec">here</a>, it
is important to make sure that exceptions thrown by C++ code do not pass
into the Python interpreter core. By default, Boost.Python translates all
C++ exceptions thrown by wrapped functions and module init functions into
Python, but the default translators are extremely limited: most C++
exceptions will appear in Python as a <a href=
"http://www.python.org/doc/current/lib/module-exceptions.html">RuntimeError</a>
exception whose representation is
<code>'Unidentifiable&nbsp;C++&nbsp;Exception'</code>. To produce better
error messages, users can register additional exception translators as
described below.</p>
<h2><a name="functions"></a>Functions</h2>
<h3><code><a name="register_exception_translator-spec">register_exception_translator</a></code></h3>
<pre>
<a name="register_exception_translator-spec">template&lt;class ExceptionType, class Translate&gt;</a>
void register_exception_translator(Translate const&amp; translate);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b></dt>
<dd>
<code>Translate</code> is <a href=
"../../../utility/CopyConstructible.html">Copyconstructible</a>, and
the following code must be well-formed:
<pre>
void f(ExceptionType x) { translate(x); }
</pre>
The expression <code>translate(x)</code> must either throw a C++
exception, or a subsequent call to <code><a href=
"http://www.python.org/doc/current/api/exceptionHandling.html">PyErr_Occurred</a>()</code>
must return 1.
</dd>
<p>
<dt><b>Effects:</b> Adds a copy of <code>translate</code> to the sequence of
exception translators tried when Boost.Python catches an exception that
is about to pass into Python's core interpreter. The new translator
will get "first shot" at translating all exceptions matching the catch
clause shown above. Any subsequently-registered translators will be
allowed to translate the exception earlier. A translator which cannot
translate a given C++ exception can re-throw it, and it will be handled
by a translator which was registered earlier (or by the default
translator).</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/def.hpp&gt;
#include &lt;boost/python/exception_translator.hpp&gt;
#include &lt;exception&gt;
struct my_exception : std::exception
{
char const* what() throw() { return "One of my exceptions"; }
};
void translate(my_exception const&amp; e)
{
// Use the Python 'C' API to set up an exception object
PyErr_SetString(PyExc_RuntimeError, e.what());
}
void something_which_throws()
{
...
throw my_exception();
...
}
BOOST_PYTHON_MODULE(exception_translator_ext)
{
using namespace boost::python;
register_exception_translator&lt;my_exception&gt;(&amp;translate);
def("something_which_throws", something_which_throws);
}
</pre>
<br>
<br>
<hr>
<p>Revised 03 October, 2002</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/extract.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#extract-spec">Class <code>extract</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#extract-spec-synopsis">Class <code>extract</code>
synopsis</a></dt>
<dt><a href="#extract-spec-ctors">Class <code>extract</code>
constructors and destructor</a></dt>
<dt><a href="#extract-spec-observers">Class
<code>extract</code> observer functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>Exposes a mechanism for extracting C++ object values from
generalized Python objects. Note that
<code>extract&lt;</code>...<code>&gt;</code> can also be used to
&quot;downcast&quot; an <a
href="object.html#object-spec">object</a> to some specific <a
href="ObjectWrapper.html#ObjectWrapper-concept">ObjectWrapper</a>. Because
invoking a mutable python type with an argument of the same type
(e.g. <code>list([1,2])</code> typically makes a <em>copy</em> of
the argument object, this may be the only way to access the <a
href="ObjectWrapper.html#ObjectWrapper-concept">ObjectWrapper</a>'s
interface on the original object.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="extract-spec"></a>Class template <code>extract</code></h3>
<p><code>extract&lt;T&gt;</code> can be used to extract a value of
an arbitrary C++ type from an instance of <code><a
href="object.html#object-spec">object</a></code>. Two usages are supported:
<ol>
<li><b><code>extract&lt;T&gt;(o)</code></b> is a temporary object
which is implicitly convertible to <code>T</code> (explicit conversion
is also available through the object's function-call
operator). However, if no conversion is available which can convert
<code>o</code> to an object of type <code>T</code>, a Python
<code>TypeError</code> exception will be <a
href="definitions.html#raise">raised</a>.
<li><b><code>extract&lt;T&gt; x(o);</code></b> constructs an extractor
whose <code>check()</code> member function can be used to ask whether
a conversion is available without causing an exception to be thrown.
</ol>
<h4><a name="extract-spec-synopsis"></a>Class template <code>extract</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class T&gt;
struct extract
{
typedef <i>unspecified</i> result_type;
extract(PyObject*);
extract(object const&amp;);
result_type operator()() const;
operator result_type() const;
bool check() const;
};
}}
</pre>
<h4><a name="extract-spec-ctors"></a>Class <code>extract</code>
constructors and destructor</h4>
<pre>
extract(PyObject* p);
extract(object const&amp;);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> The first form requires that <code>p</code> is non-null.</dt>
<dt><b>Effects:</b>Stores a pointer to the Python object managed
by its constructor argument. In particular, the reference
count of the object is not incremented. The onus is on the user
to be sure it is not destroyed before the extractor's conversion
function is called.</dt>
</dl>
<h4><a name="extract-spec-observers"></a>Class <code>extract</code>
observer functions</h4>
<pre>
result_type operator()() const;
operator result_type() const;
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> Converts the stored pointer to
<code>result_type</code>, which is either <code>T</code> or
<code>T const&amp;</code>.
</dt>
<dt><b>Returns:</b> An object of <code>result_type</code>
corresponding to the one referenced by the stored pointer.</dt>
<dt><b>Throws:</b> <code><a
href="errors.html#error_already_set-spec">error_already_set</a></code>
and sets a <code>TypeError</code> if no such conversion is
available. May also emit other unspecified exceptions thrown by
the converter which is actually used.</dt>
</dl>
<pre>
bool check() const;
</pre>
<dl class="function-semantics">
<dt><b>Postconditions:</b> None. In particular, note that a
return value of <code>true</code> does not preclude an exception
being thrown from <code>operator result_type()</code> or
<code>operator()()</code>.</dt>
<dt><b>Returns:</b> <code>false</code> <i>only</i> if no conversion from the
stored pointer to <code>T</code> is available.</dt>
</dl>
<h2><a name="examples"></a>Examples</h2>
<pre>
#include &lt;cstdio&gt;
using namespace boost::python;
int Print(str s)
{
// extract a C string from the Python string object
char const* c_str = extract&lt;char const*&gt;(s);
// Print it using printf
std::printf(&quot;%s\n&quot;, c_str);
// Get the Python string's length and convert it to an int
return extract&lt;int&gt;(s.attr(&quot;__len__&quot;)())
}
</pre>
The following example shows how extract can be used along with
<code><a
href="class.html#class_-spec">class_</a>&lt;</code>...<code>&gt;</code>
to create and access an instance of a wrapped C++ class.
<pre>
struct X
{
X(int x) : v(x) {}
int value() { return v; }
private:
int v;
};
BOOST_PYTHON_MODULE(extract_ext)
{
object x_class(
class_&lt;X&gt;(&quot;X&quot;, init&lt;int&gt;())
.def(&quot;value&quot;, &amp;X::value))
;
// Instantiate an X object through the Python interface.
// Its lifetime is now managed by x_obj.
object x_obj = x_class(3);
// Get a reference to the C++ object out of the Python object
X const&amp; x = extract&lt;X&amp;&gt;(x_obj);
assert(x.value() == 3);
}
</pre>
<p>Revised 30 September, 2002</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<title>Boost.Python - FAQ</title>
</head>
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<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
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<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Frequently Asked Questions (FAQs)</h2>
</td>
</tr>
</table>
<hr>
<dl class="page-index">
<dt><a href="#question1">Is return_internal reference
efficient?</a></dt>
<dt><a href="#question2">How can I wrap containers which take C++
containers as arguments?</a></dt>
</dl>
<h2><a name="question1"></a>Is return_internal reference efficient?</h2>
<blockquote>
<b>Q:</b> <i>I have an object composed of 12 doubles. A const&amp; to
this object is returned by a member function of another class. From the
viewpoint of using the returned object in Python I do not care if I get
a copy or a reference to the returned object. In Boost.Python Version 2
I have the choice of using copy_const_reference or
return_internal_reference. Are there considerations that would lead me
to prefer one over the other, such as size of generated code or memory
overhead?</i>
<p><b>A:</b> copy_const_reference will make an instance with storage
for one of your objects, size = base_size + 12 * sizeof(double).
return_internal_reference will make an instance with storage for a
pointer to one of your objects, size = base_size + sizeof(void*).
However, it will also create a weak reference object which goes in the
source object's weakreflist and a special callback object to manage the
lifetime of the internally-referenced object. My guess?
copy_const_reference is your friend here, resulting in less overall
memory use and less fragmentation, also probably fewer total
cycles.</p>
</blockquote>
<h2><a name="question2"></a>How can I wrap functions which take C++
containers as arguments?</h2>
<p>Ralf W. Grosse-Kunstleve provides these notes:</p>
<ol>
<li>
Using the regular <code>class_&lt;&gt;</code> wrapper:
<pre>
class_&lt;std::vector&lt;double&gt; &gt;("std_vector_double")
.def(...)
...
;
</pre>
This can be moved to a template so that several types (double, int,
long, etc.) can be wrapped with the same code. This technique is used
in the file
<blockquote>
scitbx/include/scitbx/array_family/boost_python/flex_wrapper.h
</blockquote>
in the "scitbx" package. The file could easily be modified for
wrapping std::vector&lt;&gt; instantiations.
<p>This type of C++/Python binding is most suitable for containers
that may contain a large number of elements (&gt;10000).</p>
</li>
<li>
Using custom rvalue converters. Boost.Python "rvalue converters"
match function signatures such as:
<pre>
void foo(std::vector&lt;double&gt; const&amp; array); // pass by const-reference
void foo(std::vector&lt;double&gt; array); // pass by value
</pre>
Some custom rvalue converters are implemented in the file
<blockquote>
scitbx/include/scitbx/boost_python/container_conversions.h
</blockquote>
This code can be used to convert from C++ container types such as
std::vector&lt;&gt; or std::list&lt;&gt; to Python tuples and vice
versa. A few simple examples can be found in the file
<blockquote>
scitbx/array_family/boost_python/regression_test_module.cpp
</blockquote>
Automatic C++ container &lt;-&gt; Python tuple conversions are most
suitable for containers of moderate size. These converters generate
significantly less object code compared to alternative 1 above.
</li>
</ol>
A disadvantage of using alternative 2 is that operators such as
arithmetic +,-,*,/,% are not available. It would be useful to have custom
rvalue converters that convert to a "math_array" type instead of tuples.
This is currently not implemented but is possible within the framework of
Boost.Python V2 as it will be released in the next couple of weeks. [ed.:
this was posted on 2002/03/10]
<p>It would also be useful to also have "custom lvalue converters" such
as std::vector&lt;&gt; &lt;-&gt; Python list. These converters would
support the modification of the Python list from C++. For example:</p>
<p>C++:</p>
<pre>
void foo(std::vector&lt;double&gt;&amp; array)
{
for(std::size_t i=0;i&lt;array.size();i++) {
array[i] *= 2;
}
}
</pre>
Python:
<pre>
&gt;&gt;&gt; l = [1, 2, 3]
&gt;&gt;&gt; foo(l)
&gt;&gt;&gt; print l
[2, 4, 6]
</pre>
Custom lvalue converters require changes to the Boost.Python core library
and are currently not available.
<p>P.S.:</p>
<p>The "scitbx" files referenced above are available via anonymous
CVS:</p>
<pre>
cvs -d:pserver:anonymous@cvs.cctbx.sourceforge.net:/cvsroot/cctbx login
cvs -d:pserver:anonymous@cvs.cctbx.sourceforge.net:/cvsroot/cctbx co scitbx
</pre>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
05 November, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<td valign="top">
<h1 class="c1">Boost.Python</h1>
<h2 class="c2">February 2002 Progress Report</h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="index">
<dt><a href="#Python10">Python10 Conference Report</a>
<dt><a href="#progress">Boost.Python v2 Progress</a>
<dd>
<dl class="index">
<dt><a href="#documentation">Documentation</a>
<dt><a href="#conversion">Overhaul of
<code>to_python</code>/<code>from_python</code>
conversion mechanism</a>
<dt><a href="#miscellaneous">Miscellaneous</a>
</dl>
</dl>
<h2><a name="Python10">Python10 Conference Report</a></h2>
I spent the first week of February at the Python10 conference
in Alexandria, VA. I&#39;m including this experience report
for two reasons: firstly, it documents where my time was
used. Secondly, a public presence for Boost.Python and
interaction between the Python and C++ communities is
important to the future of Boost.Python, which in turn is
important to the Kull Project.
<p>Andy Koenig, of all people, was the keynote speaker of
this year&#39;s opening plenary session. He presented his
&quot;impressions of a polyglot outsider&quot;, which
studiously avoided any mention of C++ until the end of his
talk, when he was asked about standardization. I was
surprised to learn that the C++ community at large wanted a
few more years before beginning but when ANSI accepted
HP&#39;s request for a standard, the process was forced to
start: it was a matter of participating or having
standardization proceed without one&#39;s input. Andy managed
to highlight very effectively the balance of strengths in
Python, one of the most important being its support for
extension via libraries. In many ways that makes Python a
good analogue for C++ in the interpreted world
<p>There were several kind mentions of the Boost.Python
library from people who found it indispensable. I was
particularly happy that Karl MacMillan, Michael Droettboom,
and Ichiro Fujinaga from Johns Hopkins is using it to do OCR
on a vast library of music notation, since in a previous life
I was an author of music notation software. These guys are
also drawing on Ullrich Koethe&#39;s VIGRA library for image
manipulation (Ullrich has been a major contributor to
Boost.Python). They also have a system for writing the
Boost.Python wrapper code in C++ comments, which allows them
to keep all of the code in one place. I&#39;ve asked them to
send me some information on that.
<p>The development of Swig has been gaining momentum again
(the basic description at
www.boost.org/libs/python/doc/comparisons.html still
applies). The talk given about it by David Beazly was very
well-attended, and they appear to have quite a few users.
Swig&#39;s strengths (coverage of many langauages) and
weaknesses (incomplete C++ language support) haven&#39;t
changed, although the C++ support seems to have improved
considerably - they now claim to have a complete model of the
C++ type system. It seems to be mostly geared at wrapping
what Walter Landry calls &quot;C-Tran&quot;: C++ code which
traffics in built-in types with little use of abstraction.
I&#39;m not knocking that, either: I&#39;m sure a lot of that
code exists, so it&#39;s a valuable service. One feature Swig
has which I&#39;d like to steal is the ability to unwrap a
single Python argument into multiple C++ arguments, for
example, by converting a Python string into a pointer and
length. When his talk was over, David approached me about a
possible joint workshop on language binding, which sounds
like a fun idea to me.
<p>I spent some considerable time talking with Steven Knight,
the leader of the Scons build tool effort. We had a lot to
share with one another, and I gained a much better
appreciation for many of the Scons design decisions. Scons
seems to be concentrating on being the ultimate build system
substrate, and Steve seemed to think that we were on the
right track with our high-level design. We both hope that the
Boost.Build V2 high-level architecture can eventually be
ported to run on top of Scons.
<p>They also have a highly-refined and successful development
procedure which I&#39;d like to emulate for Boost.Build V2.
Among many other things they do, their source-control system
automatically ensures that when you check in a new test, it
is automatically run on the currently checked-in state of the
code, and is expected to fail -- a relatively obvious good
idea which I&#39;ve never heard before.
<p>Guido Van Rossum&#39;s &quot;State of the Python
Union&quot; address was full of questions for the community
about what should be done next, but the one idea Guido seemed
to stress was that core language stability and continuing
library development would be a good idea (sound familiar?) I
mentioned the Boost model as a counterpoint to the idea of
something like CPAN (the massive Perl library archives), and
it seemed to generate some significant interest. I&#39;ve
offered to work with anyone from the Python community who
wants to set up something like Boost.
<p>There was some discussion of &quot;string
interpolation&quot; (variable substitution in strings), and
Guido mentioned that he had some thoughts about the
strengths/weaknesses of Python&#39;s formatting interface. It
might be useful for those working on formatting for boost to
contact him and find out what he has to say.
<p>Ka-Ping Yee demoed a Mailman discussion thread weaver.
This tool weaves the various messages in a discussion thread
into a single document so you can follow the entire
conversation. Since we&#39;re looking very seriously at
moving Boost to Mailman, this could be a really useful thing
for us to have. If we do this, we&#39;ll move the yahoogroups
discussions into the mailman archive so old discussions can
be easily accessed in the same fashion.
<p>And, just because it&#39;s cool, though perhaps not
relevant: http://homepages.ulb.ac.be/~arigo/psyco/ is a
promising effort to accelerate the execution of Python code
to speeds approaching those of compiled languages. It
reminded me a lot of Todd Veldhuizen&#39;s research into
moving parts of C++ template compilation to runtime, only
coming from the opposite end of things.
<h2><a name="progress">Boost.Python v2 Progress</a></h2>
Here&#39;s what actually got accomplished.
<h3><a name="documentation">Documentation</a></h3>
<p>My first priority upon returning from Python10 was to get
some documentation in place. After wasting an unfortunate
amount of time looking at automatic documentation tools which
don&#39;t quite work, I settled down to use Bill Kempf&#39;s
HTML templates designed to be a boost standard. While they
are working well, it is highly labor-intensive.
<p>I decided to begin with the high-level reference material,
as opposed to tutorial, narrative, or nitty-gritty details of
the framework. It seemed more important to have a precise
description of the way the commonly-used components work than
to have examples in HTML (since we already have some test
modules), and since the low-level details are much
less-frequently needed by users it made sense for me to
simply respond to support requests for the time being.
<p>After completing approximately 60% of the high-level docs
(currently checked in to libs/python/doc/v2), I found myself
ready to start documenting the mechanisms for creating
to-/from-python converters. This caused a dilemma: I had
realized during the previous week that a much simpler,
more-efficient, and easier-to-use implementation was
possible, but I hadn&#39;t planned on implementing it right
away, since what was already in place worked adequately. I
had also received my first query on the C++-sig about how to
write such a converter
<p>Given the labor-intensive nature of documentation writing,
I decided it would be a bad idea to document the conversion
mechanism if I was just going to rewrite it. Often the best
impetus for simplifying a design is the realization that
understandably documenting its current state would be too
difficult, and this was no exception.
<h3><a name="conversion">Overhaul of
<code>to_python</code>/<code>from_python</code> conversion
mechanism</a></h3>
<p>There were two basic realizations involved here:
<ol>
<li><code>to_python</code> conversion could be a one-step
process, once an appropriate conversion function is found.
This allows elimination of the separate indirect
convertibility check
<li>There are basically two categories of from_python
conversions: those which lvalues stored within or held by
the Python object (essentially extractions), like what
happens when an instance of a C++ class exposed with class_
is used as the target of a wrapped member function), and
those in which a new rvalue gets created, as when a Python
Float is converted to a C++
<code>complex&lt;double&gt;</code> or a Python tuple is
converted to a C++ <code>std::vector&lt;&gt;</code>. From
the client side, there are two corresponding categories of
conversion: those which demand an lvalue conversion and
those which can accept an lvalue or an rvalue conversion.
</ol>
The latter realization allowed the following collapse, which
considerably simplified things:
<blockquote>
<table border="1" summary="Conversion protocol">
<tr>
<th>Target Type
<th>Eligible Converters
<tr>
<td><code>T</code>
<td rowspan="5"><code>T</code> rvalue or lvalue
<tr>
<td><code>T const</code>
<tr>
<td><code>T volatile</code>
<tr>
<td><code>T const volatile</code>
<tr>
<td><code>T const&amp;</code>
<tr>
<td><code>T const*</code>
<td rowspan="9"><code>T</code> lvalue
<tr>
<td><code>T volatile*</code>
<tr>
<td><code>T const volatile*</code>
<tr>
<td><code>T&amp;</code>
<tr>
<td><code>T volatile&amp;</code>
<tr>
<td><code>T const volatile&amp;</code>
<tr>
<td><code>T* const&amp;</code>
<tr>
<td><code>T const* const&amp;</code>
<tr>
<td><code>T volatile*const&amp;</code>
<tr>
<td><code>T const volatile*const&amp;</code>
</table>
</blockquote>
This job included the following additional enhancements:
<ul>
<li>Elimination of virtual functions, which cause object
code bloat
<li>Registration of a single converter function for all
lvalue conversions, two for all rvalue conversions
<li>Killed lots of unneeded code
<li>Increased opacity of registry interface
<li>Eliminated all need for decorated runtime type
identifiers
<li>Updated test modules to reflect new interface
<li>Eliminated the need for users to worry about converter
lifetime issues Additional Builtin Conversion Enhancements
<li>Support for complex&lt;float&gt;,
complex&lt;double&gt;, and complex&lt;long double&gt;
conversions
<li>Support for bool conversions
<li>NULL pointers representable by None in Python
<li>Support for conversion of Python classic classes to
numeric types
</ul>
<h3><a name="miscellaneous">Miscellaneous</a></h3>
These don&#39;t fit easily under a large heading:
<ul>
<li>Support CallPolicies for class member functions
<li>from_python_data.hpp: revamped type alignment
metaprogram so that it&#39;s fast enough for KCC
<li>classfwd.hpp header forward-declares class_&lt;T&gt;
<li>indirect_traits.hpp:
<li>added is_pointer_to_reference
<li>fixed bugs
<li>Reduced recompilation dependencies
<li>msvc_typeinfo works around broken MS/Intel typeid()
implementation
<li>Many fixes and improvements to the type_traits library
in order to work around compiler bugs and suppress warnings
<li>Eliminated the need for explicit acquisition of
converter registrations
<li>Expanded constructor support to 6 arguments
<li>Implemented generalized pointer lifetime support
<li>Updated code generation for returning.hpp
<li>Tracked down and fixed cycle GC bugs
<li>Added comprehensive unit tests for destroy_reference,
pointer_type_id, select_from_python, complex&lt;T&gt;,
bool, and classic class instance conversions
</ul>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
4 April, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p class="c3">&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a>
2002. All Rights Reserved.

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<title>Boost.Python - &lt;boost/python/from_python.hpp&gt;</title>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
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<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/from_python.hpp&gt;</h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a>
<dt><a href="#classes">Classes</a>
<dd>
<dl class="page-index">
<dt><a href="#from_python-spec">Class
Template<code>from_python</code></a>
<dd>
<dl class="page-index">
<dt><a href="#from_python-spec-synopsis">Class Template
<code>from_python</code> synopsis</a>
<dt><a href="#from_python-spec-ctors">Class Template
<code>from_python</code> constructor</a>
<dt><a href="#from_python-spec-observers">Class Template
<code>from_python</code> observer functions</a>
</dl>
</dl>
<dt><a href="#examples">Example</a>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/from_python.hpp&gt;</code> introduces a class
template <code>from_python&lt;T&gt;</code> for extracting a C++ object of
type <code>T</code> from a Python object.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="from_python-spec"></a>Class Template
<code>from_python&lt;class T&gt;</code></h3>
<p><code>from_python&lt;T&gt;</code> is the type used internally by
Boost.Python to extract C++ function arguments from a Python argument tuple
when calling a wrapped function. It can also be used directly to make
similar conversions in other contexts.
<h4><a name="from_python-spec-synopsis"></a>Class Template
<code>from_python</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class T&gt;
struct from_python : private <a href=
"../../../utility/utility.htm#Class noncopyable">boost::noncopyable</a> // Exposition only.
// from_python&lt;T&gt; meets the <a href=
"NonCopyable.html">NonCopyable</a> requirements
{
from_python(PyObject*);
bool convertible() const;
<i>convertible-to-T</i> operator()(PyObject*) const;
};
}
</pre>
<h4><a name="from_python-spec-ctors"></a>Class Template
<code>from_python</code> constructor</h4>
<pre>
from_python(PyObject* p);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>p != 0</code>
<dt><b>Effects:</b> Constructs a <code>from_python</code> object suitable
for extracting a C++ object of type <code>T</code> from <code>p</code>.
</dl>
<h4><a name="from_python-spec-observers"></a>Class Template
<code>from_python</code> observer functions</h4>
<pre>
bool convertible() const;
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>false</code> if the conversion cannot succeed.
This indicates that either:
<dd>
<ol>
<li>No <code>from_python_converter</code> was registered for
<code>T</code>, or
<li>any such converter rejected the constructor argument
<code>p</code> by returning <code>0</code> from its
<code>convertible()</code> function
</ol>
Note that conversion may still fail in <code>operator()</code> due to
an exception.
<dt><b>Throws:</b> nothing
<dt><b>Rationale:</b> Because <code>from_python&lt;&gt;</code> is used in
overload resolution, and throwing an exception can be slow, it is useful
to be able to rule out a broad class of unsuccessful conversions without
throwing an exception.
</dl>
<pre>
<i>convertible-to-T</i> operator()(PyObject* p) const;
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>*p</code> refers to the same object which was
passed to the constructor, and <code>convertible()</code> returns
<code>true</code>.
<dt><b>Effects:</b> performs the conversion
<dt><b>Returns:</b> an object convertible to <code>T</code>.
</dl>
<h2><a name="examples"></a>Example</h2>
<pre>
#include &lt;string&gt;
#include &lt;boost/python/from_python.hpp&gt;
// If a std::string can be extracted from p, return its
// length. Otherwise, return 0.
std::size_t length_if_string(PyObject* p)
{
from_python&lt;std::string&gt; converter(p);
if (!converter.convertible())
return 0;
else
return converter(p).size();
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
05 November, 2001
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>

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<h3><a href="../../../../index.htm"><img height="86" width="277"
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<h1 class="c1">Boost.Python</h1>
<h2 class="c2">Header &lt;boost/python/handle.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#handle-spec">Class template
<code>handle</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#handle-spec-synopsis">Class <code>handle</code>
synopsis</a></dt>
<dt><a href="#handle-spec-ctors">Class <code>handle</code>
constructors and destructor</a></dt>
<dt><a href="#handle-spec-modifiers">Class <code>handle</code>
modifier functions</a></dt>
<dt><a href="#handle-spec-observers">Class <code>handle</code>
observer functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#borrowed-spec"><code>borrowed</code></a></dt>
<dt><a href="#allow_null-spec"><code>allow_null</code></a></dt>
</dl>
</dd>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/handle.hpp&gt;</code> provides
<code>class&nbsp;template&nbsp;handle</code>, a smart pointer for
managing reference-counted Python objects.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="handle-spec"></a>Class template <code>handle</code></h3>
<p><code>handle</code> is a smart pointer to a Python object type; it
holds a pointer of type <code>T*</code>, where T is its template
parameter. <code>T</code> must be either a type derived from
<code>PyObject</code> or a <a href="definitions.html#POD">POD</a>
type whose initial <code>sizeof(PyObject)</code> bytes are
layout-compatible with <code>PyObject</code>. Use
<code>handle&lt;&gt;</code> at the boundary between tehe
Python/'C' API and high-level code; prefer <code><a
href="object.html#object-spec">object</a></code> for a generalized
interface to Python objects.
<p><a name="upcast"></a>In this document, the term "upcast" refers to an
operation which converts a pointer <code>Y*</code> to a base class
pointer <code>T*</code> via <code>static_cast&lt;T*&gt;</code> if
<code>Y</code> is derived from <code>T</code>, or via C-style cast
<code>(T*)</code> if it is not. However, in the latter case the "upcast"
is ill-formed if the initial <code>sizeof(PyObject)</code> bytes of
<code>Y</code> are not layout-compatible with <code>PyObject</code>.</p>
<h4><a name="handle-spec-synopsis"></a>Class template handle
synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class T&gt;
class handle
{
typedef <i>unspecified-member-function-pointer</i> bool_type;
public: // types
typedef T element_type;
public: // member functions
~handle();
template &lt;class Y&gt;
explicit handle(detail::borrowed&lt;null_ok&lt;Y&gt; &gt;* p);
template &lt;class Y&gt;
explicit handle(null_ok&lt;detail::borrowed&lt;Y&gt; &gt;* p);
template &lt;class Y&gt;
explicit handle(detail::borrowed&lt;Y&gt;* p);
template &lt;class Y&gt;
explicit handle(null_ok&lt;Y&gt;* p);
template &lt;class Y&gt;
explicit handle(Y* p);
handle();
handle&amp; operator=(handle const&amp; r);
template&lt;typename Y&gt;
handle&amp; operator=(handle&lt;Y&gt; const &amp; r); // never throws
template &lt;typename Y&gt;
handle(handle&lt;Y&gt; const&amp; r);
handle(handle const&amp; r);
T* operator-&gt; () const;
T&amp; operator* () const;
T* get() const;
T* release();
operator bool_type() const; // never throws
private:
T* m_p;
};
template &lt;class T&gt; struct null_ok;
namespace detail { template &lt;class T&gt; struct borrowed; }
}}
</pre>
<h4><a name="handle-spec-ctors">Class <code>handle</code> constructors
and destructor</a></h4>
<pre>
virtual ~handle();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> <code>Py_XDECREF(m_p)</code></dt>
</dl>
<pre>
template &lt;class Y&gt;
explicit handle(detail::borrowed&lt;null_ok&lt;Y&gt; &gt;* p);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> <code>Py_XDECREF(m_p)</code></dt>
</dl>
<pre>
template &lt;class Y&gt;
explicit handle(null_ok&lt;detail::borrowed&lt;Y&gt; &gt;* p);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>m_p&nbsp;=&nbsp;</code><i>upcast</i><code>&lt;T*&gt;(p);</code></dt>
</dl>
<pre>
template &lt;class Y&gt;
explicit handle(detail::borrowed&lt;Y&gt;* p);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>m_p&nbsp;=&nbsp;</code><i>upcast</i><code>&lt;T*&gt;(<a href=
"errors.html#expect_non_null-spec">expect_non_null</a>(p));</code></dt>
</dl>
<pre>
template &lt;class Y&gt;
explicit handle(null_ok&lt;Y&gt;* p);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>Py_XINCREF(p);&nbsp;m_p&nbsp;=&nbsp;</code><i>upcast</i><code>&lt;T*&gt;(p);</code></dt>
</dl>
<pre>
template &lt;class Y&gt;
explicit handle(Y* p);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>Py_XINCREF(p);&nbsp;m_p&nbsp;=&nbsp;</code><i>upcast</i><code>&lt;T*&gt;(<a
href=
"errors.html#expect_non_null-spec">expect_non_null</a>(p));</code></dt>
</dl>
<pre>
handle();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> <code>m_p&nbsp;=&nbsp;0;</code></dt>
</dl>
<pre>
template &lt;typename Y&gt;
handle(handle&lt;Y&gt; const&amp; r);
handle(handle const&amp; r);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>m_p&nbsp;=&nbsp;r.m_p;&nbsp;Py_XINCREF(m_p);</code></dt>
</dl>
<h4><a name="handle-spec-modifiers">Class <code>handle</code>
modifiers</a></h4>
<pre>
handle&amp; operator=(handle const&amp; r);
template&lt;typename Y&gt;
handle&amp; operator=(handle&lt;Y&gt; const &amp; r); // never throws
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>Py_XINCREF(r.m_p);&nbsp;Py_XDECREF(m_p);&nbsp;m_p&nbsp;=&nbsp;r.m_p;</code></dt>
</dl>
<pre>
T* release();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> <code>T* x = m_p;&nbsp;m_p&nbsp;=&nbsp;0;return
x;</code></dt>
</dl>
<h4><a name="handle-spec-observers">Class <code>handle</code>
observers</a></h4>
<pre>
T* operator-&gt; () const;
T* get() const;
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>m_p;</code></dt>
</dl>
<pre>
T&amp; operator* () const;
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>*m_p;</code></dt>
</dl>
<pre>
operator bool_type() const; // never throws
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> 0 if <code>m_p&nbsp;==&nbsp;0</code>, a pointer
convertible to <code>true</code> otherwise.</dt>
</dl>
<h2><a name="functions"></a>Functions</h2>
<h3><a name="borrowed-spec"></a><code>borrowed</code></h3>
<pre>
template <class T>
detail::borrowed<T>* borrowed(T* p)
{
return (detail::borrowed<T>*)p;
}
</pre>
<h3><a name="allow_null-spec"></a><code>allow_null</code></h3>
<pre>
template <class T>
null_ok<T>* allow_null(T* p)
{
return (null_ok<T>*)p;
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
03 October, 2002 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p class="c4">&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
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<h1 class="c1">Boost.Python</h1>
<h2 class="c2">Header
&lt;boost/python/has_back_reference.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#has_back_reference-spec">Class template
<code>has_back_reference</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#has_back_reference-spec-synopsis">Class template
<code>has_back_reference</code> synopsis</a></dt>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
</dd>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/has_back_reference.hpp&gt;</code> defines the
traits class template <code>has_back_reference&lt;&gt;</code>, which can
be specialized by the user to indicate that a wrapped class instance
holds a <code>PyObject*</code> corresponding to a Python object.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="has_back_reference-spec"></a>Class template
<code>has_back_reference</code></h3>
<p>A unary metafunction whose <code>value</code> is true iff its argument
is a <code>pointer_wrapper&lt;&gt;</code>.</p>
<h4><a name="has_back_reference-spec-synopsis"></a>Class template
<code>has_back_reference</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template&lt;class WrappedClass&gt; class has_back_reference
{
static <i>unspecified</i> value = false;
};
}}
</pre>
<p>A "<a href="../../../../more/generic_programming.html#traits">traits
class</a>" which is inspected by Boost.Python to determine how wrapped
classes can be constructed.</p>
<dl class="traits-semantics">
<dt><code>value</code> is an integral constant convertible to bool of
unspecified type.</dt>
<dt>Specializations may substitute a value convertible to
<code>true</code> for <code>value</code> iff for each invocation of
<code>class_&lt;WrappedClass&gt;::def(init&lt;</code><i>type-sequence...</i><code>
&gt;())</code>, there exists a corresponding constructor
<code>WrappedClass::WrappedClass(PyObject*,&nbsp;</code><i>type-sequence...</i>
<code>)</code>. If such a specialization exists, the
<code>WrappedClass</code> constructors will be called with a "back
reference" pointer to the corresponding Python object whenever they are
invoked from Python.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<h3>C++ module definition</h3>
<pre>
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/has_back_reference.hpp&gt;
#include &lt;boost/python/handle.hpp&gt;
#include &lt;boost/shared_ptr.hpp&gt;
using namespace boost::python;
struct X
{
X(PyObject* self) : m_self(self), m_x(0) {}
X(PyObject* self, int x) : m_self(self), m_x(x) {}
handle&lt;&gt; self() { return handle&lt;&gt;(borrowed(m_self)); }
int get() { return m_x; }
void set(int x) { m_x = x; }
PyObject* m_self;
int x;
};
// specialize has_back_reference for X
namespace boost { namespace python
{
template &lt;&gt;
struct has_back_reference&lt;X&gt;
{
enum { value = true; }
}
}}
struct Y
{
Y() : m_x(0) {}
Y(int x) : m_x(x) {}
int get() { return m_x; }
void set(int x) { m_x = x; }
int x;
};
boost::shared_ptr&lt;Y&gt; Y_self(boost::shared_ptr&lt;Y&gt; self) const { return self; }
BOOST_PYTHON_MODULE(back_references)
{
class_&lt;X&gt;("X")
.def(init&lt;int&gt;())
.def("self", &amp;X::self)
.def("get", &amp;X::get)
.def("set", &amp;X::set)
;
class_&lt;Y, shared_ptr&lt;Y&gt; &gt;("Y")
.def(init&lt;int&gt;())
.def("get", &amp;Y::get)
.def("set", &amp;Y::set)
.def("self", Y_self)
;
}
</pre>
The following Python session illustrates that <code>x.self()</code>
returns the same Python object on which it is invoked, while
<code>y.self()</code> must create a new Python object which refers to the
same Y instance.
<h3>Python code</h3>
<pre>
&gt;&gt;&gt; from back_references import *
&gt;&gt;&gt; x = X(1)
&gt;&gt;&gt; x2 = x.self()
&gt;&gt;&gt; x2 is x
<b>1</b>
&gt;&gt;&gt; (x.get(), x2.get())
(1, 1)
&gt;&gt;&gt; x.set(10)
&gt;&gt;&gt; (x.get(), x2.get())
(10, 10)
&gt;&gt;&gt;
&gt;&gt;&gt;
&gt;&gt;&gt; y = Y(2)
&gt;&gt;&gt; y2 = y.self()
&gt;&gt;&gt; y2 is y
<b>0</b>
&gt;&gt;&gt; (y.get(), y2.get())
(2, 2)
&gt;&gt;&gt; y.set(20)
&gt;&gt;&gt; (y.get(), y2.get())
(20, 20)
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p class="c3">&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</p>
</body>
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<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
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<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;{{header}}&gt;</h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a>
<dt><a href="#macros">Macros</a>
<dd>
<dl class="page-index">
<dt><a href="#macro-spec">{{macro name}}</a>
</dl>
<dt><a href="#values">Values</a>
<dd>
<dl class="page-index">
<dt><a href="#value-spec">{{value name}}</a>
</dl>
<dt><a href="#types">Types</a>
<dd>
<dl class="page-index">
<dt><a href="#type-spec">{{type name}}</a>
</dl>
<dt><a href="#classes">Classes</a>
<dd>
<dl class="page-index">
<dt><a href="#class-spec">Class <code>{{name}}</code></a>
<dd>
<dl class="page-index">
<dt><a href="#class-spec-synopsis">Class <code>{{name}}</code> synopsis</a>
<dt><a href="#class-spec-ctors">Class <code>{{name}}</code>
constructors and destructor</a>
<dt><a href="#class-spec-comparisons">Class <code>{{name}}</code> comparison functions</a>
<dt><a href="#class-spec-modifiers">Class <code>{{name}}</code> modifier functions</a>
<dt><a href="#class-spec-observers">Class <code>{{name}}</code> observer functions</a>
<dt><a href="#class-spec-statics">Class <code>{{name}}</code> static functions</a>
</dl>
</dl>
<dt><a href="#functions">Functions</a>
<dd>
<dl class="page-index">
<dt><a href="#function-spec">{{function name}}</a>
</dl>
<dt><a href="#objects">Objects</a>
<dd>
<dl class="page-index">
<dt><a href="#object-spec">{{object name}}</a>
</dl>
<dt><a href="#examples">Example(s)</a>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>{{Introductory text}}
<h2><a name="macros"></a>Macros</h2>
<p><a name="macro-spec"></a>{{Macro specifications}}
<h2><a name="values"></a>Values</h2>
<p><a name="value-spec"></a>{{Value specifications}}
<h2><a name="types"></a>Types</h2>
<p><a name="type-spec"></a>{{Type specifications}}
<h2><a name="classes"></a>Classes</h2>
<h3><a name="class-spec"></a>Class <code>{{name}}</code></h3>
<p>{{class overview text}}
<h4><a name="class-spec-synopsis"></a>Class <code>{{name}}</code> synopsis</h4>
<pre>
namespace boost
{
class {{name}}
{
};
};
</pre>
<h4><a name="class-spec-ctors"></a>Class <code>{{name}}</code> constructors and
destructor</h4>
<pre>
{{constructor}}
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> {{text}}
<dt><b>Effects:</b> {{text}}
<dt><b>Postconditions:</b> {{text}}
<dt><b>Returns:</b> {{text}}
<dt><b>Throws:</b> {{text}}
<dt><b>Complexity:</b> {{text}}
<dt><b>Rationale:</b> {{text}}
</dl>
<pre>
{{destructor}}
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> {{text}}
<dt><b>Effects:</b> {{text}}
<dt><b>Postconditions:</b> {{text}}
<dt><b>Returns:</b> {{text}}
<dt><b>Throws:</b> {{text}}
<dt><b>Complexity:</b> {{text}}
<dt><b>Rationale:</b> {{text}}
</dl>
<h4><a name="class-spec-comparisons"></a>Class <code>{{name}}</code> comparison
functions</h4>
<pre>
{{function}}
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> {{text}}
<dt><b>Effects:</b> {{text}}
<dt><b>Postconditions:</b> {{text}}
<dt><b>Returns:</b> {{text}}
<dt><b>Throws:</b> {{text}}
<dt><b>Complexity:</b> {{text}}
<dt><b>Rationale:</b> {{text}}
</dl>
<h4><a name="class-spec-modifiers"></a>Class <code>{{name}}</code> modifier
functions</h4>
<pre>
{{function}}
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> {{text}}
<dt><b>Effects:</b> {{text}}
<dt><b>Postconditions:</b> {{text}}
<dt><b>Returns:</b> {{text}}
<dt><b>Throws:</b> {{text}}
<dt><b>Complexity:</b> {{text}}
<dt><b>Rationale:</b> {{text}}
</dl>
<h4><a name="class-spec-observers"></a>Class <code>{{name}}</code> observer
functions</h4>
<pre>
{{function}}
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> {{text}}
<dt><b>Effects:</b> {{text}}
<dt><b>Postconditions:</b> {{text}}
<dt><b>Returns:</b> {{text}}
<dt><b>Throws:</b> {{text}}
<dt><b>Complexity:</b> {{text}}
<dt><b>Rationale:</b> {{text}}
</dl>
<h4><a name="class-spec-statics"></a>Class <code>{{name}}</code> static functions</h4>
<pre>
{{function}}
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> {{text}}
<dt><b>Effects:</b> {{text}}
<dt><b>Postconditions:</b> {{text}}
<dt><b>Returns:</b> {{text}}
<dt><b>Throws:</b> {{text}}
<dt><b>Complexity:</b> {{text}}
<dt><b>Rationale:</b> {{text}}
</dl>
<h2><a name="functions"></a>Functions</h2>
<pre>
<a name="function-spec"></a>{{function}}
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> {{text}}
<dt><b>Effects:</b> {{text}}
<dt><b>Postconditions:</b> {{text}}
<dt><b>Returns:</b> {{text}}
<dt><b>Throws:</b> {{text}}
<dt><b>Complexity:</b> {{text}}
<dt><b>Rationale:</b> {{text}}
</dl>
<h2><a name="objects"></a>Objects</h2>
<p><a name="object-spec"></a>{{Object specifications}}
<h2><a name="examples"></a>Example(s)</h2>
<p>{{Example(s)}}
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
05 November, 2001
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>

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<title>Boost.Python - &lt;boost/python/implicit.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/implicit.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#implicitly_convertible-spec">Function Template
<code>implicitly_convertible</code></a></dt>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<code>implicitly_convertible</code> allows Boost.Python to implicitly
take advantage of a C++ implicit or explicit conversion when matching
Python objects to C++ argument types.
<h2><a name="functions"></a>Functions</h2>
<h3><a name="implicitly_convertible-spec"></a>Function template
<code>implicitly_convertible</code></h3>
<pre>
template &lt;class Source, class Target&gt;
void implicitly_convertible();
</pre>
<table border="1" summary="implicitly_convertible template parameters">
<caption>
<b><code>implicitly_convertible</code> template parameters</b><br>
</caption>
<tr>
<th>Parameter</th>
<th>Description</th>
</tr>
<tr>
<td><code>Source</code></td>
<td>The source type of the implicit conversion</td>
</tr>
<tr>
<td><code>Target</code></td>
<td>The target type of the implicit conversion</td>
</tr>
</table>
<dl class="function-semantics">
<dt><b>Requires:</b> The declaration <code>Target t(s);</code>, where
<code>s</code> is of type <code>Source</code>, is valid.</dt>
<dt><b>Effects:</b> registers an rvalue <code>from_python</code>
converter to <code>Target</code> which can succeed for any
<code>PyObject*&nbsp;p</code> iff there exists any registered converter
which can produce <code>Source</code> rvalues</dt>
<dt><b>Rationale:</b> C++ users expect to be able to take advantage of
the same sort of interoperability in Python as they do in C++.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<h3>C++ module definition</h3>
<pre>
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/implicit.hpp&gt;
#include &lt;boost/python/module.hpp&gt;
using namespace boost::python;
struct X
{
X(int x) : v(x) {}
operator int() { return v; }
int v;
};
int x_value(X const&amp; x)
{
return x.v;
}
X make_x(int n) { return X(n); }
BOOST_PYTHON_MODULE(implicit_ext)
{
def("x_value", x_value);
def("make_x", make_x);
class_&lt;X&gt;("X",
init&lt;int&gt;())
;
implicitly_convertible&lt;X,int&gt;();
implicitly_convertible&lt;int,X&gt;();
}
</pre>
<h3>Python code</h3>
<pre>
&gt;&gt;&gt; from implicit_ext import *
&gt;&gt;&gt; x_value(X(42))
42
&gt;&gt;&gt; x_value(42)
42
&gt;&gt;&gt; x = make_x(X(42))
&gt;&gt;&gt; x_value(x)
42
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<h1 align="center">Boost.Python</h1>
<h2 align="center">Headers &lt;boost/python/init.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href=
"#init-expressions"><em>init-expressions</em></a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#init-spec">Class template <code>init</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#init-spec-synopsis">Class template
<code>init</code> synopsis</a></dt>
<dt><a href="#init-spec-ctors">Class <code>init</code>
constructors</a></dt>
</dl>
</dd>
<dt><a href="#optional-spec">Class template
<code>optional</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#optional-spec-synopsis">Class template
<code>optional</code> synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/init.hpp&gt;</code> defines the interface for
exposing C++ constructors to Python as extension class
<code>__init__</code> functions.</p>
<h2><a name="init-expressions"><em>init-expressions</em></a></h2>
An <em>init-expression</em> is used to describe a family of
<code>__init__</code> methods to be generated for an extension class, and
the result has the following properties:
<blockquote>
<dl class="properties">
<dt><b>docstring:</b> An <a href="definitions.html#ntbs">ntbs</a>
whose value will bound to the method's <code>__doc__</code>
attribute</dt>
<dt><b>keywords:</b> A <a href=
"args.html#keyword-expression">keyword-expression</a> which will be
used to name (a trailing subsequence of) the arguments to the
generated <code>__init__</code> function(s).</dt>
<dt><b>call policies:</b> An instance of a model of <a href=
"CallPolicies.html">CallPolicies</a>.</dt>
<dt><b>argument types:</b> An MPL sequence of C++ argument types
which will be used to construct the wrapped C++ object. An init
expression has one or more
<b>valid prefixes</b> which are given by a sequence of
prefixes of its argument types.</dt>
</dl>
</blockquote>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="init-spec"></a>Class template <code>init&lt;T1 =</code>
<i>unspecified</i><code>,&nbsp;T2 =</code>
<i>unspecified</i><code>,</code>...<code>Tn</code> =
<i>unspecified</i><code>&gt;</code></h3>
<p>A <a href="../../../mpl/doc/ref/Sequences.html">MPL sequence</a> which
can be used to specify a family of one or more <code>__init__</code>
functions. Only the last <code>T</code><i><small>i</small></i> supplied
may be an instantiation of <a href=
"#optional-spec"><code>optional</code></a><code>&lt;</code>...<code>&gt;</code>.</p>
<h4><a name="init-spec-synopsis"></a>Class template <code>init</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;T1 = <i>unspecified</i>,...T<i>n</i> = <i>unspecified</i>&gt;
struct init
{
init(char const* doc = 0);
template &lt;class Keywords&gt; init(Keywords const&amp; kw, char const* doc = 0);
template &lt;class Keywords&gt; init(char const* doc, Keywords const&amp; kw);
template &lt;class CallPolicies&gt;
<em>unspecified</em> operator[](CallPolicies const&amp; policies) const
};
}}
</pre>
<h4><a name="init-spec-ctors"></a>Class template <code>init</code>
constructors</h4>
<pre>
init(char const* doc = 0);
template &lt;class Keywords&gt; init(Keywords const&amp; kw, char const* doc = 0);
template &lt;class Keywords&gt; init(char const* doc, Keywords const&amp; kw);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> If supplied, <code>doc</code> is an <a href=
"definitions.html#ntbs">ntbs</a>. If supplied, <code>kw</code> is the
result of a <a href="args.html#keyword-expression"></a></dt>
<dt><b>Effects:</b> The result is an <em>init-expression</em> whose
<em>docstring</em> is <code>doc</code> and whose <em>keywords</em> are
a reference to <code>kw</code>. If the first form is used, the
resulting expression's <em>keywords</em> are empty. The expression's
<em>call policies</em> are an instance of <a href=
"default_call_policies.html#default_call_policies-spec">default_call_policies</a>.
If <code>T</code><i><small>n</small></i> is <a href=
"#optional-spec"><code>optional</code></a><code>&lt;U1,&nbsp;U2,</code>...
<code>U</code><small><i>m</i></small><code>&gt;</code>, the
expression's <em>valid prefixes</em> are given by:</dt>
<dd>
<blockquote>
(<code>T1,&nbsp;T2,</code>...<code>T</code><i><small>n-1</small></i>),
(<code>T1,&nbsp;T2,</code>...<code>T</code><i><small>n-1</small></i>
<code>,&nbsp;U1</code>),
(<code>T1,&nbsp;T2,</code>...<code>T</code><i><small>n-1</small></i>
<code>,&nbsp;U1,&nbsp;U2</code>),
...(<code>T1,&nbsp;T2,</code>...<code>T</code><i><small>n-1</small></i>
<code>,&nbsp;U1,&nbsp;U2,</code>...<code>U</code><i><small>m</small></i>).
</blockquote>
Otherwise, the expression has one <em>valid prefix</em> given by the
the template arguments the user specified.
</dd>
</dl>
<h4><a name="init-spec-observers"></a>Class template <code>init</code>
observer functions</h4>
<pre>
template &lt;class Policies&gt;
<em>unspecified</em> operator[](Policies const&amp; policies) const
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> Policies is a model of <a href=
"CallPolicies.html">CallPolicies</a>.</dt>
<dt><b>Effects:</b> Returns a new <a href=
"#init-expressions"><em>init-expression</em></a> with all the same
properties as the <code>init</code> object except that its <em>call
policies</em> are replaced by a reference to
<code>policies</code>.</dt>
</dl>
<h3><a name="optional-spec"></a>Class template <code>optional&lt;T1
=</code> <i>unspecified</i><code>,&nbsp;T2 =</code>
<i>unspecified</i><code>,</code>...<code>Tn</code> =
<i>unspecified</i><code>&gt;</code></h3>
<p>A <a href="../../../mpl/doc/ref/Sequences.html">MPL sequence</a> which
can be used to specify the optional arguments to an <code>__init__</code>
function.</p>
<h4><a name="optional-spec-synopsis"></a>Class template
<code>optional</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;T1 = <i>unspecified</i>,...T<i>n</i> = <i>unspecified</i>&gt;
struct optional {};
}}
</pre>
<h2><a name="examples"></a>Example(s)</h2>
<p>Given the C++ declarations:</p>
<pre>
class Y;
class X
{
public:
X(int x, Y* y) : m_y(y) {}
X(double);
private:
Y* m_y;
};
</pre>
A corresponding Boost.Python extension class can be created with:
<pre>
using namespace boost::python;
class_&lt;X&gt;("X", "This is X's docstring.",
init&lt;int,char const*&gt;(args("x","y"), "X.__init__'s docstring")[
with_custodian_and_ward&lt;1,3&gt;()]
)
.def(init&lt;double&gt;())
;
</pre>
<hr>
Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
1 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
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<td valign="top">
<h1 class="c1">Boost.Python</h1>
<h2 class="c2">Header &lt;boost/python/instance_holder.hpp&gt;</h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a>
<dt><a href="#classes">Classes</a>
<dd>
<dl class="page-index">
<dt><a href="#instance_holder-spec">Class
<code>instance_holder</code></a>
<dd>
<dl class="page-index">
<dt><a href="#instance_holder-spec-synopsis">Class
<code>instance_holder</code> synopsis</a>
<dt><a href="#instance_holder-spec-ctors">Class
<code>instance_holder</code> destructor</a>
<dt><a href="#instance_holder-spec-modifiers">Class
<code>instance_holder</code> modifier functions</a>
<dt><a href="#instance_holder-spec-observers">Class
<code>instance_holder</code> observer functions</a>
</dl>
</dl>
<dt><a href="#examples">Example</a>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/instance_holder.hpp&gt;</code> provides
<code>class&nbsp;instance_holder</code>, the base class for types
which hold C++ instances of wrapped classes.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="instance_holder-spec"></a>Class <code>instance_holder</code></h3>
<p><code>instance_holder</code> is an abstract base class whose
concrete derived classes hold C++ class instances within their
Python object wrappers. To allow multiple inheritance in Python
from C++ class wrappers, each such Python object contains a chain
of <code>instance_holder</code>s. When an <code>__init__</code>
function for a wrapped C++ class is invoked, a new
<code>instance_holder</code> instance is created and installed in
the Python object using its <code><a
href="#instance_holder-spec-modifiers">install</a></code>()
function. Each concrete class derived from
<code>instance_holder</code> must provide a <code><a
href="#instance_holder-spec-observers">holds</a>()</code>
implementation which allows Boost.Python to query it for the
type(s) it is holding. In order to support the held type's wrapped
constructor(s), the class must also provide constructors that can
accept an initial <code>PyObject*</code> argument referring to the
owning Python object, and which forward the rest of their
arguments to the constructor of the held type. The initial
argument is needed to enable virtual function overriding in
Python, and may be ignored, depending on the specific
<code>instance_holder</code> subclass.
<h4><a name="instance_holder-spec-synopsis"></a>Class instance_holder
synopsis</h4>
<pre>
namespace boost { namespace python
{
class instance_holder : <a href="../../../utility/utility.htm#Class noncopyable">noncopyable</a>
{
public:
// destructor
virtual ~instance_holder();
// instance_holder modifiers
void install(PyObject* inst) throw();
// instance_holder observers
virtual void* holds(type_info) = 0;
};
}}
</pre>
<h4><a name="instance_holder-spec-ctors">Class <code>instance_holder</code>
destructor</a></h4>
<pre>
virtual ~instance_holder();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> destroys the object
</dl>
<h4><a name="instance_holder-spec-modifiers">Class
<code>instance_holder</code> modifiers</a></h4>
<pre>
void install(PyObject* inst) throw();
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>inst</code> is a Python instance of a
wrapped C++ class type, or is a type derived from a wrapped C++
class type.
<dt><b>Effects:</b> installs the new instance at the head of the
Python object's chain of held instances.
<dt><b>Throws:</b> nothing
</dl>
<h4><a name="instance_holder-spec-observers">Class <code>instance_holder</code>
observers</a></h4>
<pre>
virtual void* holds(type_info x) = 0;
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> A pointer to an object of the type described
by <code>x</code> if <code>*this</code> contains such an object,
0 otherwise.
</dl>
<h2><a name="examples"></a>Example</h2>
The following is a simplified version of the instance holder template
used by Boost.Python to wrap classes held by smart pointers:
<pre>
template &lt;class SmartPtr, class Value&gt;
struct pointer_holder : instance_holder
{
// construct from the SmartPtr type
pointer_holder(SmartPtr p)
:m_p(p)
// Forwarding constructors for the held type
pointer_holder(PyObject*)
:m_p(new Value())
{
}
template&lt;class A0&gt;
pointer_holder(PyObject*,A0 a0)
:m_p(new Value(a0))
{
}
template&lt;class A0,class A1&gt;
pointer_holder(PyObject*,A0 a0,A1 a1)
:m_p(new Value(a0,a1))
{
}
...
private: // required holder implementation
void* holds(type_info dst_t)
{
// holds an instance of the SmartPtr type...
if (dst_t == python::type_id&lt;SmartPtr&gt;())
return &amp;this-&gt;m_p;
// ...and an instance of the SmartPtr's element_type, if the
// pointer is non-null
return python::type_id&lt;Value&gt;() == dst_t ? &amp;*this-&gt;m_p : 0;
}
private: // data members
SmartPtr m_p;
};
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 May, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p class="c4">&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All
Rights Reserved.

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<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/iterator.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#iterator-spec">Class template
<code>iterator</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#iterator-spec-synopsis">Class
<code>iterator</code> synopsis</a></dt>
<dt><a href="#iterator-spec-ctors">Class template
<code>iterator</code> constructor</a></dt>
</dl>
</dd>
</dl>
<dl class="page-index">
<dt><a href="#iterators-spec">Class template
<code>iterators</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#iterators-spec-synopsis">Class
<code>iterators</code> synopsis</a></dt>
<dt><a href="#iterators-spec-types">Class template
<code>iterators</code> nested types</a></dt>
<dt><a href="#iterators-spec-statics">Class template
<code>iterators</code> static functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#range-spec">range</a></dt>
</dl>
</dd>
<dt><a href="#examples">Examples</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/iterator.hpp&gt;</code> provides types and
functions for creating <a href=
"http://www.python.org/doc/current/lib/typeiter.html">Python
iterators</a> from <a href=
"http://www.sgi.com/tech/stl/Container.html">C++ Containers</a> and <a
href="http://www.sgi.com/tech/stl/Iterators.html">Iterators</a>. Note
that if your <code>class_</code> supports random-access iterators,
implementing <code><a href=
"http://www.python.org/doc/current/ref/sequence-types.html#l2h-128">__getitem__</a></code>
(also known as the Sequence Protocol) may serve you better than using
this facility: Python will automatically create an iterator type for you
(see <a href=
"http://www.python.org/doc/current/lib/built-in-funcs.html#l2h-35">iter()</a>),
and each access can be range-checked, leaving no possiblity of accessing
through an invalidated C++ iterator.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="iterator-spec"></a>Class Template <code>iterator</code></h3>
<p>Instances of <code>iterator&lt;C,P&gt;</code> hold a reference to a
callable Python object which, when invoked from Python, expects a single
argument <code>c</code> convertible to <code>C</code> and creates a
Python iterator that traverses [<code>c.begin()</code>,
<code>c.end()</code>). The optional <a href=
"CallPolicies.html">CallPolicies</a> <code>P</code> can be used to
control how elements are returned during iteration.</p>
<p>In the table below, <code><b>c</b></code> is an instance of
<code>Container</code>.</p>
<table border="1" summary="iterator template parameters">
<tr>
<th>Template Parameter</th>
<th>Requirements</th>
<th>Semantics</th>
<th>Default</th>
</tr>
<tr>
<td><code>Container</code></td>
<td>[c.begin(),c.end()) is a valid <a href=
"http://www.sgi.com/tech/stl/Iterators.html">Iterator range</a>.</td>
<td>The result will convert its argument to <code>c</code> and call
<code>c.begin()</code> and <code>c.end()</code> to acquire iterators.
To invoke <code>Container</code>'s <code>const</code>
<code>begin()</code> and <code>end()</code> functions, make it
<code>const</code>.</td>
</tr>
<tr>
<td><code>NextPolicies</code></td>
<td>A default-constructible model of <a href=
"CallPolicies.html#CallPolicies-concept">CallPolicies</a>.</td>
<td>Applied to the resulting iterators' <code>next()</code>
method.</td>
<td>An unspecified model of <a href=
"CallPolicies.html#CallPolicies-concept">CallPolicies</a> which
always makes a copy of the result of deferencing the underlying C++
iterator</td>
</tr>
</table>
<h4><a name="iterator-spec-synopsis"></a>Class Template iterator
synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class Container
, class NextPolicies = <i>unspecified</i>&gt;
struct iterator : <a href="object.html#object-spec">object</a>
{
iterator();
};
}}
</pre>
<h4><a name="iterator-spec-constructors"></a>Class Template iterator
constructor</h4>
<pre>
iterator()
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b></dt>
<dd>
Initializes its base class with the result of:
<pre>
range&lt;NextPolicies&gt;(&amp;iterators&lt;Container&gt;::begin, &amp;iterators&lt;Container&gt;::end)
</pre>
</dd>
<dt><b>Postconditions:</b> <code>this-&gt;get()</code> points to a
Python callable object which creates a Python iterator as described
above.</dt>
<dt><b>Rationale:</b> Provides an easy way to create iterators for the
common case where a C++ class being wrapped provides
<code>begin()</code> and <code>end()</code>.</dt>
</dl>
<!-- -->
<h3><a name="iterators-spec"></a>Class Template
<code>iterators</code></h3>
<p>A utility class template which provides a way to reliably call its
argument's <code>begin()</code> and <code>end()</code> member functions.
Note that there is no portable way to take the address of a member
function of a C++ standard library container, so
<code>iterators&lt;&gt;</code> can be particularly helpful when wrapping
them.</p>
<p>In the table below, <code><b>x</b></code> is an instance of
<code>C</code>.</p>
<table border="1" summary="iterator template parameters">
<tr>
<th>Required Valid Expression</th>
<th>Type</th>
</tr>
<tr>
<td><code>x.begin()</code></td>
<td>Convertible to <code>C::const_iterator</code> if <code>C</code>
is a <code>const</code> type; convertible to <code>C::iterator</code>
otherwise.</td>
</tr>
<tr>
<td><code>x.end()</code></td>
<td>Convertible to <code>C::const_iterator</code> if <code>C</code>
is a <code>const</code> type; convertible to <code>C::iterator</code>
otherwise.</td>
</tr>
</table>
<h4><a name="iterators-spec-synopsis"></a>Class Template iterators
synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class C&gt;
struct iterators
{
typedef typename C::[const_]iterator iterator;
static iterator begin(C&amp; x);
static iterator end(C&amp; x);
};
}}
</pre>
<h4><a name="iterators-spec-types"></a>Class Template iterators nested
types</h4>
If C is a <code>const</code> type,
<pre>
typedef typename C::const_iterator iterator;
</pre>
Otherwise:
<pre>
typedef typename C::iterator iterator;
</pre>
<h4><a name="iterators-spec-statics"></a>Class Template iterators static
functions</h4>
<pre>
static iterator begin(C&amp;);
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>x.begin()</code></dt>
</dl>
<pre>
static iterator end(C&amp;);
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>x.end()</code></dt>
</dl>
<!-- -->
<h2><a name="functions"></a>Functions</h2>
<pre>
<a name=
"range-spec">template</a> &lt;class NextPolicies, class Target, class Accessor1, class Accessor2&gt;
<a href=
"object.html#object-spec">object</a> range(Accessor1 start, Accessor2 finish);
template &lt;class NextPolicies, class Accessor1, class Accessor2&gt;
<a href=
"object.html#object-spec">object</a> range(Accessor1 start, Accessor2 finish);
template &lt;class Accessor1, class Accessor2&gt;
<a href=
"object.html#object-spec">object</a> range(Accessor1 start, Accessor2 finish);
</pre>
<dl class="range-semantics">
<dt><b>Requires:</b> <code>NextPolicies</code> is a
default-constructible model of <a href=
"CallPolicies.html#CallPolicies-concept">CallPolicies</a>.</dt>
<dt><b>Effects:</b></dt>
<dd>
<dl>
<dt>The first form creates a Python callable object which, when
invoked, converts its argument to a <code>Target</code> object
<code>x</code>, and creates a Python iterator which traverses
[<code><a href=
"../../../bind/bind.html">bind</a>(start,_1)(x)</code>,&nbsp;<code><a
href="../../../bind/bind.html">bind</a>(finish,_1)(x)</code>),
applying <code>NextPolicies</code> to the iterator's
<code>next()</code> function.</dt>
<dt>The second form is identical to the first, except that
<code>Target</code> is deduced from <code>Accessor1</code> as
follows:</dt>
<dd>
<ol>
<li>If <code>Accessor1</code> is a function type,
<code>Target</code> is the type of its first argument.</li>
<li>If <code>Accessor1</code> is a data member pointer of the
form <code>R&nbsp;(T::*)</code>, <code>Target</code> is
identical to <code>T</code>.</li>
<li>If <code>Accessor1</code> is a member function pointer of
the form
<code>R&nbsp;(T::*)(</code><i>arguments...</i><code>)</code>&nbsp;
<i>cv-opt</i>, where <i>cv-opt</i> is an optional
<code>cv-qualifier</code>, <code>Target</code> is identical to
<code>T</code>.</li>
</ol>
</dd>
<dt>The third form is identical to the second, except that
<code>NextPolicies</code> is an unspecified model of <a href=
"CallPolicies.html#CallPolicies-concept">CallPolicies</a> which
always makes a copy of the result of deferencing the underlying C++
iterator</dt>
</dl>
</dd>
<dt><b>Rationale:</b> The use of <code><a href=
"../../../bind/bind.html">boost::bind</a>()</code> allows C++ iterators
to be accessed through functions, member functions or data member
pointers. Customization of <code>NextPolicies</code> (e.g. using
<code><a href=
"return_internal_reference.html#return_internal_reference-spec">return_internal_reference</a></code>)
is useful when it is expensive to copy sequence elements of a wrapped
class type. Customization of <code>Target</code> is useful when
<code>Accessor1</code> is a function object, or when a base class of
the intended target type would otherwise be deduced.</dt>
</dl>
<h2><a name="examples"></a>Examples</h2>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;vector&gt;
using namespace boost::python;
BOOST_PYTHON_MODULE(demo)
{
class_&lt;std::vector&lt;double&gt; &gt;("dvec")
.def("__iter__", iterator&lt;std::vector&lt;double&gt; &gt;())
;
}
</pre>
A more comprehensive example can be found in:
<dl>
<dt><code><a href=
"../../test/iterator.cpp">libs/python/test/iterator.cpp</a></code></dt>
<dt><code><a href=
"../../test/input_iterator.cpp">libs/python/test/input_iterator.cpp</a></code></dt>
<dt><code><a href=
"../../test/iterator.py">libs/python/test/input_iterator.py</a></code></dt>
<dd>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All
Rights Reserved.</i></p>
</dd>
</dl>
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<tr>
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<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/list.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#list-spec">Class <code>list</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#list-spec-synopsis">Class <code>list</code>
synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>Exposes a <a href=
"ObjectWrapper.html#TypeWrapper-concept">TypeWrapper</a> for the Python
<a href=
"http://www.python.org/doc/current/lib/typesseq-mutable.html">list</a>
type.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="list-spec"></a>Class <code>list</code></h3>
<p>Exposes the <a href=
"http://www.python.org/doc/current/lib/typesseq-mutable.html">mapping
protocol</a> of Python's built-in <code>list</code> type. The semantics
of the constructors and member functions defined below can be fully
understood by reading the <a href=
"ObjectWrapper.html#TypeWrapper-concept">TypeWrapper</a> concept
definition. Since <code>list</code> is publicly derived from <code><a
href="object.html#object-spec">object</a></code>, the public object
interface applies to <code>list</code> instances as well.</p>
<h4><a name="list-spec-synopsis"></a>Class <code>list</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
class list : public object
{
public:
list(); // new list
template &lt;class T&gt;
explicit list(T const&amp; sequence);
template &lt;class T&gt;
void append(T const&amp; x);
template &lt;class T&gt;
long count(T const&amp; value) const;
template &lt;class T&gt;
void extend(T const&amp; x);
template &lt;class T&gt;
long index(T const&amp; x) const;
template &lt;class T&gt;
void insert(object const&amp; index, T const&amp; x); // insert object before index
object pop(); // remove and return item at index (default last)
object pop(long index);
object pop(object const&amp; index);
template &lt;class T&gt;
void remove(T const&amp; value);
void reverse(); // reverse *IN PLACE*
void sort(); // sort *IN PLACE*; if given, cmpfunc(x, y) -&gt; -1, 0, 1
template &lt;class T&gt;
void sort(T const&amp; value);
};
}}
</pre>
<h2><a name="examples"></a>Example</h2>
<pre>
using namespace boost::python;
// Return the number of zeroes in the list
long zeroes(list l)
{
return l.count(0);
}
</pre>
<p>Revised 1 October, 2002</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/long.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#long_-spec">Class <code>long_</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#long_-spec-synopsis">Class <code>long_</code>
synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>Exposes a <a href=
"ObjectWrapper.html#TypeWrapper-concept">TypeWrapper</a> for the Python
<a href=
"http://www.python.org/doc/current/lib/typesnumeric.html">long</a>
integer type.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="long_-spec"></a>Class <code>long_</code></h3>
<p>Exposes the <a href=
"http://www.python.org/doc/current/lib/typesnumeric.html">numeric type
protocol</a> of Python's built-in <code>long</code> type. The semantics
of the constructors and member functions defined below can be fully
understood by reading the <a href=
"ObjectWrapper.html#TypeWrapper-concept">TypeWrapper</a> concept
definition. Since <code>long_</code> is publicly derived from <code><a
href="object.html#object-spec">object</a></code>, the public object
interface applies to <code>long_</code> instances as well.</p>
<h4><a name="long_-spec-synopsis"></a>Class <code>long_</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
class long_ : public object
{
public:
long_(); // new long_
template &lt;class T&gt;
explicit long_(T const&amp; rhs);
template &lt;class T, class U&gt;
long_(T const&amp; rhs, U const&amp; base);
};
}}
</pre>
<h2><a name="examples"></a>Example</h2>
<pre>
namespace python = boost::python;
// compute a factorial without overflowing
python::long_ fact(long n)
{
if (n == 0)
return python::long_(1);
else
return n * fact(n - 1);
}
</pre>
<p>Revised 1 October, 2002</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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</html>

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<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;boost/python/lvalue_from_python.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/lvalue_from_pytype.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#lvalue_from_pytype-spec">Class Template
<code>lvalue_from_pytype</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#lvalue_from_pytype-spec-synopsis">Class Template
<code>lvalue_from_pytype</code> synopsis</a></dt>
<dt><a href="#lvalue_from_pytype-spec-ctors">Class Template
<code>lvalue_from_pytype</code> constructor</a></dt>
</dl>
</dd>
</dl>
<dl class="page-index">
<dt><a href="#extract_identity-spec">Class Template
<code>extract_identity</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#extract_identity-spec-synopsis">Class Template
<code>extract_identity</code> synopsis</a></dt>
<dt><a href="#extract_identity-spec-statics">Class Template
<code>extract_identity</code> static functions</a></dt>
</dl>
</dd>
<dt><a href="#extract_member-spec">Class Template
<code>extract_member</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#extract_member-spec-synopsis">Class Template
<code>extract_member</code> synopsis</a></dt>
<dt><a href="#extract_member-spec-statics">Class Template
<code>extract_member</code> static functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<code>&lt;boost/python/lvalue_from_pytype.hpp&gt;</code> supplies a
facility for extracting C++ objects from within Python instances of a
given type. This is typically useful for dealing with "traditional"
Python extension types.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="lvalue_from_pytype-spec"></a>Class template
<code>lvalue_from_pytype</code></h3>
<p>Class template <code>lvalue_from_pytype</code> will register
from_python converters which, given an object of the given Python type,
can extract references and pointers to a particular C++ type. Its
template arguments are:</p>
<table border="1" summary="lvalue_from_pytype template parameters">
<caption>
<b><code>lvalue_from_pytype</code> Requirements</b><br>
In the table below, <b><code>x</code></b> denotes an object of type
<code>PythonObject&amp;</code>
</caption>
<tr>
<th>Parameter</th>
<th>Requirements</th>
<th>Semantics</th>
</tr>
<tr>
<td><code>Extractor</code></td>
<td>a model of <a href=
"Extractor.html#Extractor-concept">Extractor</a> whose execute
function returns a reference type.</td>
<td>Extracts the lvalue from the Python object once its type has been
confirmed</td>
</tr>
<tr>
<td><code>python_type</code></td>
<td>A compile-time constant <code><a href=
"http://www.python.org/doc/2.2/ext/dnt-type-methods.html">PyTypeObject</a>*</code></td>
<td>The Python type of instances convertible by this converter.
Python subtypes are also convertible.</td>
</tr>
</table>
<h4><a name="lvalue_from_pytype-spec-synopsis"></a>Class template
<code>lvalue_from_pytype</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class Extractor, PyTypeObject const* python_type&gt;
struct lvalue_from_pytype
{
lvalue_from_pytype();
};
}}
</pre>
<h4><a name="lvalue_from_pytype-spec-ctors"></a>Class template
<code>lvalue_from_pytype</code> constructor</h4>
<pre>
lvalue_from_pytype();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> Registers converters which can convert Python
objects of the given type to lvalues of the type returned by
<code>Extractor::execute</code>.</dt>
</dl>
<h3><a name="extract_identity-spec"></a>Class template
<code>extract_identity</code></h3>
<p><code>extract_identity</code> is a model of <a href=
"Extractor.html#Extractor-concept">Extractor</a> which can be used in the
common case where the C++ type to be extracted is the same as the Python
object type.</p>
<h4><a name="extract_identity-spec-synopsis"></a>Class template
<code>extract_identity</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class InstanceType&gt;
struct extract_identity
{
static InstanceType&amp; execute(InstanceType&amp; c);
};
}}
</pre>
<h4><a name="extract_identity-spec-statics"></a>Class template
<code>extract_identity</code> static functions</h4>
<pre>
InstanceType&amp; execute(InstanceType&amp; c);
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>c</code></dt>
</dl>
<h3><a name="extract_member-spec"></a>Class template
<code>extract_member</code></h3>
<p><code>extract_member</code> is a model of <a href=
"Extractor.html#Extractor-concept">Extractor</a> which can be used in the
common case in the common case where the C++ type to be extracted is a
member of the Python object.</p>
<h4><a name="extract_member-spec-synopsis"></a>Class template
<code>extract_member</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class InstanceType, class MemberType, MemberType (InstanceType::*member)&gt;
struct extract_member
{
static MemberType&amp; execute(InstanceType&amp; c);
};
}}
</pre>
<h4><a name="extract_member-spec-statics"></a>Class template
<code>extract_member</code> static functions</h4>
<pre>
static MemberType&amp; execute(InstanceType&amp; c);
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>c.*member</code></dt>
</dl>
<h2><a name="examples"></a>Example</h2>
This example presumes that someone has implemented the standard <a href=
"http://www.python.org/doc/2.2/ext/dnt-basics.html">noddy example
module</a> from the Python documentation, and we want to build a module
which manipulates <code>Noddy</code>s. Since
<code>noddy_NoddyObject</code> is so simple that it carries no
interesting information, the example is a bit contrived: it assumes you
want to keep track of one particular object for some reason. This module
would have to be dynamically linked to the module which defines
<code>noddy_NoddyType</code>.
<h3>C++ module definition</h3>
<pre>
#include &lt;boost/python/reference.hpp&gt;
#include &lt;boost/python/module.hpp&gt;
// definition lifted from the Python docs
typedef struct {
PyObject_HEAD
} noddy_NoddyObject;
using namespace boost::python;
static reference&lt;PyObject&gt; cache;
bool is_cached(noddy_NoddyObject* x)
{
return x == cache.get();
}
void set_cache(noddy_NoddyObject* x)
{
cache.reset((PyObject*)x, ref::increment_count);
}
BOOST_PYTHON_MODULE(noddy_cache)
{
def("is_cached", is_cached);
def("set_cache", set_cache);
// register Noddy lvalue converter
lvalue_from_pytype&lt;extract_identity&lt;noddy_NoddyObject&gt;,&amp;noddy_NoddyType&gt;();
}
</pre>
<h3>Python code</h3>
<pre>
&gt;&gt;&gt; import noddy
&gt;&gt;&gt; n = noddy.new_noddy()
&gt;&gt;&gt; import noddy_cache
&gt;&gt;&gt; noddy_cache.is_cached(n)
0
&gt;&gt;&gt; noddy_cache.set_cache(n)
&gt;&gt;&gt; noddy_cache.is_cached(n)
1
&gt;&gt;&gt; noddy_cache.is_cached(noddy.new_noddy())
0
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September, 2001
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

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<head>
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<title>Boost.Python - &lt;boost/python/make_function.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/make_function.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#make_function-spec">make_function</a></dt>
<dt><a href="#make_constructor-spec">make_constructor</a></dt>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code><a href="#make_function-spec">make_function</a>()</code> and
<code><a href="#make_constructor-spec">make_constructor</a>()</code> are
the functions used internally by <code><a href=
"def.html#def-spec">def</a>()</code> and <code>class_&lt;&gt;::<a href=
"class.html#class_-spec-modifiers">def</a>()</code> to produce Python
callable objects which wrap C++ functions and member functions.</p>
<h2><a name="functions"></a>Functions</h2>
<pre>
<a name="make_function-spec">template &lt;class F&gt;</a>
<a href="object.html#object-spec">object</a> make_function(F f)
template &lt;class F, class Policies&gt;
<a href=
"object.html#object-spec">object</a> make_function(F f, Policies const&amp; policies)
template &lt;class F, class Policies, class Keywords&gt;
<a href=
"object.html#object-spec">object</a> make_function(F f, Policies const&amp; policies, Keywords const&amp; keywords)
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>F</code> is a function pointer or member
function pointer type. If <code>policies</code> are supplied, it must
be a model of <a href="CallPolicies.html">CallPolicies</a>. If
<code>kewords</code> are supplied, it must be the result of a <a href=
"args.html#keyword-expression"><em>keyword-expression</em></a>
specifying no more arguments than the <a href=
"definitions.html#arity">arity</a> of <code>f</code>.</dt>
<dt><b>Effects:</b> Creates a Python callable object which, when called
from Python, converts its arguments to C++ and calls <code>f</code>. If
<code>F</code> is a pointer-to-member-function type, the target object
of the function call (<code>*this</code>) will be taken from the first
Python argument, and subsequent Python arguments will be used as the
arguments to <code>f</code>. If <code>policies</code> are supplied, it
will be applied to the function as described <a href=
"CallPolicies.html">here</a>. If <code>keywords</code> are
supplied, the keywords will be applied in order to the final
arguments of the resulting function.</dt>
<dt><b>Returns:</b> An instance of <a href=
"object.html#object-spec">object</a> which holds the new Python
callable object.</dt>
</dl>
<pre>
<a name=
"make_constructor-spec"></a>template &lt;class T, class ArgList, class Generator&gt;
<a href="object.html#object-spec">object</a> make_constructor();
template &lt;class ArgList, class Generator, class Policies&gt;
<a href=
"object.html#object-spec">object</a> make_constructor(Policies const&amp; policies)
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>T</code> is a class type.
<code>Policies</code> is a model of <a href=
"CallPolicies.html">CallPolicies</a>. <code>ArgList</code> is an <a
href="../../../mpl/doc/Sequences.html">MPL sequence</a> of C++ argument
types (<i>A1,&nbsp;A2,...&nbsp;AN</i>) such that if
<code>a1,&nbsp;a2</code>...&nbsp;<code>aN</code> are objects of type
<i>A1,&nbsp;A2,...&nbsp;AN</i> respectively, the expression <code>new
Generator::apply&lt;T&gt;::type(a1,&nbsp;a2</code>...&nbsp;<code>aN</code>)
is valid. Generator is a model of <a href=
"HolderGenerator.html">HolderGenerator</a>.</dt>
<dt><b>Effects:</b> Creates a Python callable object which, when called
from Python, expects its first argument to be a Boost.Python extension
class object. It converts its remaining its arguments to C++ and passes
them to the constructor of a dynamically-allocated
<code>Generator::apply&lt;T&gt;::type</code> object, which is then
installed in the extension class object. In the second form, the
<code>policies</code> are applied to the arguments and result (<a href=
"http://www.python.org/doc/current/lib/bltin-null-object.html">None</a>)
of the Python callable object</dt>
<dt><b>Returns:</b> An instance of <a href=
"object.html#object-spec">object</a> which holds the new Python
callable object.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<p>C++ function exposed below returns a callable object wrapping one of
two functions.</p>
<pre>
#include &lt;boost/python/make_function.hpp&gt;
#include &lt;boost/python/module.hpp&gt;
char const* foo() { return "foo"; }
char const* bar() { return "bar"; }
using namespace boost::python;
object choose_function(bool selector)
{
if (selector)
return boost::python::make_function(foo);
else
return boost::python::make_function(bar);
}
BOOST_PYTHON_MODULE(make_function_test)
{
def("choose_function", choose_function);
}
</pre>
It can be used this way in Python:
<pre>
&gt;&gt;&gt; from make_function_test import *
&gt;&gt;&gt; f = choose_function(1)
&gt;&gt;&gt; g = choose_function(0)
&gt;&gt;&gt; f()
'foo'
&gt;&gt;&gt; g()
'bar'
</pre>
<p>
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<title>Boost.Python - &lt;boost/python/manage_new_object.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/manage_new_object.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#manage_new_object-spec">Class
<code>manage_new_object</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#manage_new_object-spec-synopsis">Class
<code>manage_new_object</code> synopsis</a></dt>
<dt><a href="#manage_new_object-spec-metafunctions">Class
<code>manage_new_object</code> metafunctions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="manage_new_object-spec"></a>Class
<code>manage_new_object</code></h3>
<p><code>manage_new_object</code> is a model of <a href=
"ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a>
which can be used to wrap C++ functions which return a pointer to an
object allocated with a <i>new-expression</i>, and expect the caller to
take responsibility for deleting that object.</p>
<h4><a name="manage_new_object-spec-synopsis"></a>Class
<code>manage_new_object</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
struct manage_new_object
{
template &lt;class T&gt; struct apply;
};
}}
</pre>
<h4><a name="manage_new_object-spec-metafunctions"></a>Class
<code>manage_new_object</code> metafunctions</h4>
<pre>
template &lt;class T&gt; struct apply
</pre>
<dl class="metafunction-semantics">
<dt><b>Requires:</b> <code>T</code> is <code>U*</code> for some
<code>U</code>.</dt>
<dt><b>Returns:</b> <code>typedef <a href=
"to_python_indirect.html#to_python_indirect-spec">to_python_indirect</a>&lt;T&gt;
type;</code></dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<p>In C++:</p>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/manage_new_object.hpp&gt;
#include &lt;boost/python/return_value_policy.hpp&gt;
struct Foo {
Foo(int x) : x(x){}
int get_x() { return x; }
int x;
};
Foo* make_foo(int x) { return new Foo(x); }
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
def("make_foo", make_foo, return_value_policy&lt;manage_new_object&gt;())
class_&lt;Foo&gt;("Foo")
.def("get_x", &amp;Foo::get_x)
;
}
</pre>
In Python:
<pre>
&gt;&gt;&gt; from my_module import *
&gt;&gt;&gt; f = make_foo(3) # create a Foo object
&gt;&gt;&gt; f.get_x()
3
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

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<meta name="generator" content="HTML Tidy, see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;boost/python/module.hpp&gt;</title>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/module.hpp&gt;</h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a>
<dt><a href="#macros">Macros</a>
<dd>
<dl class="page-index">
<dt><a href=
"#BOOST_PYTHON_MODULE-spec">BOOST_PYTHON_MODULE</a>
</dl>
<dt><a href="#examples">Example(s)</a>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>This header provides the basic facilities needed to create a
Boost.Python extension module.
<h2><a name="macros"></a>Macros</h2>
<p><a name=
"BOOST_PYTHON_MODULE-spec"><code>BOOST_PYTHON_MODULE(name)</code></a>
is used to declare Python <a href=
"http://www.python.org/doc/2.2/ext/methodTable.html#SECTION003400000000000000000">
module initialization functions</a>. The <code>name</code> argument must
exactly match the name of the module to be initialized, and must conform to
Python's <a href=
"http://www.python.org/doc/2.2/ref/identifiers.html">identifier naming
rules</a>. Where you would normally write
<pre>
extern &quot;C&quot; void init<i>name</i>()
{
...
}
</pre>
Boost.Python modules should be initialized with
<pre>
BOOST_PYTHON_MODULE(<i>name</i>)
{
...
}
</pre>
This macro generates two functions in the scope where it is used:
<code>extern&nbsp;&quot;C&quot;&nbsp;void&nbsp;init<i>name</i>()</code>,
and <code>void&nbsp;init_module_<i>name</i>()</code>, whose body must
follow the macro invocation. <code>init_<i>name</i></code> passes
<code>init_module_<i>name</i></code> to <code><a
href="errors.html#handle_exception">handle_exception</a>()</code> so
that any C++ exceptions generated are safely processeed. During the
body of <code>init_<i>name</i></code>, the current <code><a
href="scope.html#scope-spec">scope</a></code> refers to the module
being initialized.
<h2><a name="examples"></a>Example(s)</h2>
<p>C++ module definition:
<pre>
#include &lt;boost/python/module.hpp&gt;
BOOST_PYTHON_MODULE(xxx)
{
throw &quot;something bad happened&quot;
}
</pre>
Interactive Python:
<pre>
&gt;&gt;&gt; import xxx
Traceback (most recent call last):
File "<stdin>", line 1, in ?
RuntimeError: Unidentifiable C++ Exception
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
2 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>

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<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/numeric.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#array-spec">Class <code>array</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#array-spec-synopsis">Class <code>array</code>
synopsis</a></dt>
<dt><a href="#array-spec-observers">Class <code>array</code>
observer functions</a></dt>
<dt><a href="#array-spec-statics">Class <code>array</code>
static functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>Exposes a <a href=
"ObjectWrapper.html#TypeWrapper-concept">TypeWrapper</a> for the Python
<a href=
"http://www.python.org/dev/doc/devel/lib/typesmapping.html">array</a>
type.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="array-spec"></a>Class <code>array</code></h3>
<p>Provides access to the array types of <a href=
"http://www.pfdubois.com/numpy/">Numerical Python</a>'s <a href=
"http://www.pfdubois.com/numpy/#Numeric">Numeric</a> and <a href=
"http://stsdas.stsci.edu/numarray/index.html">NumArray</a> modules. With
the exception of the functions documented <a href=
"#array-spec-observers">below</a>, the semantics of the constructors and
member functions defined below can be fully understood by reading the <a
href="ObjectWrapper.html#TypeWrapper-concept">TypeWrapper</a> concept
definition. Since <code>array</code> is publicly derived from <code><a
href="object.html#object-spec">object</a></code>, the public object
interface applies to <code>array</code> instances as well.</p>
<p><a name="default_search"></a>The default behavior is to use
<code>Numeric.ArrayType</code> as the associated Python type if the
<code>Numeric</code> module is installed in the default location.
Otherwise it falls back to use <code>numarray.NDArray</code>. If neither
extension module is installed, conversions to arguments of type
<code>numeric::array</code> will cause overload resolution to reject the
overload, and other attempted uses of <code>numeric::array</code> will <a
href="definitions.html#raise">raise</a> an appropriate Python exception.
The associated Python type can be set manually using the <code><a href=
"#array-spec-statics">set_module_and_type</a>(...)</code> static
function.</p>
<h4><a name="array-spec-synopsis"></a>Class <code>array</code>
synopsis</h4>
<pre>
namespace boost { namespace python { namespace numeric
{
class array : public object
{
public:
object astype();
template &lt;class Type&gt;
object astype(Type const&amp; type_);
template &lt;class Type&gt;
object new_(Type const&amp; type_) const;
template &lt;class Sequence&gt;
void resize(Sequence const&amp; x);
void resize(long x1);
void resize(long x1, long x2);
...
void resize(long x1, long x2,...long x<i>n</i>);
template &lt;class Sequence&gt;
void setshape(Sequence const&amp; x);
void setshape(long x1);
void setshape(long x1, long x2);
...
void setshape(long x1, long x2,...long x<i>n</i>);
template &lt;class Indices, class Values&gt;
void put(Indices const&amp; indices, Values const&amp; values);
template &lt;class Sequence&gt;
object take(Sequence const&amp; sequence, long axis = 0);
template &lt;class File&gt;
void tofile(File const&amp; f) const;
object factory();
template &lt;class Buffer&gt;
object factory(Buffer const&amp;);
template &lt;class Buffer, class Type&gt;
object factory(Buffer const&amp;, Type const&amp;);
template &lt;class Buffer, class Type, class Shape&gt;
object factory(Buffer const&amp;, Type const&amp;, Shape const&amp;, bool copy = true, bool savespace = false);
template &lt;class Buffer, class Type, class Shape&gt;
object factory(Buffer const&amp;, Type const&amp;, Shape const&amp;, bool copy, bool savespace, char typecode);
template &lt;class T1&gt;
explicit array(T1 const&amp; x1);
template &lt;class T1, class T2&gt;
explicit array(T1 const&amp; x1, T2 const&amp; x2);
...
template &lt;class T1, class T2,...class T<i>n</i>&gt;
explicit array(T1 const&amp; x1, T2 const&amp; x2,...T<i>n</i> const&amp; xn);
static void set_module_and_type();
static void set_module_and_type(char const* package_path = 0, char const* type_name = 0);
object argmax(long axis=-1);
object argmin(long axis=-1);
object argsort(long axis=-1);
void byteswap();
object copy() const;
object diagonal(long offset = 0, long axis1 = 0, long axis2 = 1) const;
void info() const;
bool is_c_array() const;
bool isbyteswapped() const;
void sort();
object trace(long offset = 0, long axis1 = 0, long axis2 = 1) const;
object type() const;
char typecode() const;
object getflat() const;
long getrank() const;
object getshape() const;
bool isaligned() const;
bool iscontiguous() const;
long itemsize() const;
long nelements() const;
object nonzero() const;
void ravel();
object repeat(object const&amp; repeats, long axis=0);
void setflat(object const&amp; flat);
void swapaxes(long axis1, long axis2);
str tostring() const;
void transpose(object const&amp; axes = object());
object view() const;
};
}}}
</pre>
<h4><a name="array-spec-observers"></a>Class <code>array</code> observer
functions</h4>
<pre>
object factory();
template &lt;class Buffer&gt;
object factory(Buffer const&amp;);
template &lt;class Buffer, class Type&gt;
object factory(Buffer const&amp;, Type const&amp;);
template &lt;class Buffer, class Type, class Shape&gt;
object factory(Buffer const&amp;, Type const&amp;, Shape const&amp;, bool copy = true, bool savespace = false);
template &lt;class Buffer, class Type, class Shape&gt;
object factory(Buffer const&amp;, Type const&amp;, Shape const&amp;, bool copy, bool savespace, char typecode);
</pre>
These functions map to the underlying array type's <code>array()</code>
function family. They are not called "<code>array</code>" because of the
C++ limitation that you can't define a member function with the same name
as its enclosing class.
<pre>
template &lt;class Type&gt;
object new_(Type const&amp;) const;
</pre>
This function maps to the underlying array type's <code>new()</code>
function. It is not called "<code>new</code>" because that is a keyword
in C++.
<h4><a name="array-spec-statics"></a>Class <code>array</code> static
functions</h4>
<pre>
static void set_module_and_type(char const* package_path, char const* type_name);
static void set_module_and_type();
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>package_path</code> and
<code>type_name</code>, if supplied, is an <a href=
"definitions.html#ntbs">ntbs</a>.</dt>
<dt><b>Effects:</b> The first form sets the package path of the module
which supplies the type named by <code>type_name</code> to
<code>package_path</code>. The second form restores the <a href=
"#default_search">default search behavior</a>. The associated Python
type will be searched for only the first time it is needed, and
thereafter the first time it is needed after an invocation of
<code>set_module_and_type</code>.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<pre>
#include &lt;boost/python/numeric.hpp&gt;
#include &lt;boost/python/tuple.hpp&gt;
// sets the first element in a 2d numeric array
void set_first_element(numeric::array&amp; y, double value)
{
y[make_tuple(0,0)] = value;
}
</pre>
<p>Revised 03 October, 2002</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<title>Boost.Python - &lt;boost/python/object.hpp&gt;</title>
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<tr>
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<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/object.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#types">Types</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#slice_nil-spec">slice_nil</a></dt>
</dl>
</dd>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#const_attribute_policies-spec">Class
<code>const_attribute_policies</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#const_attribute_policies-spec-synopsis">Class
<code>const_attribute_policies</code> synopsis</a></dt>
<dt><a href="#const_attribute_policies-spec-statics">Class
<code>const_attribute_policies</code> static functions</a></dt>
</dl>
</dd>
<dt><a href="#attribute_policies-spec">Class
<code>attribute_policies</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#attribute_policies-spec-synopsis">Class
<code>attribute_policies</code> synopsis</a></dt>
<dt><a href="#attribute_policies-spec-statics">Class
<code>attribute_policies</code> static functions</a></dt>
</dl>
</dd>
<dt><a href="#const_item_policies-spec">Class
<code>const_item_policies</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#const_item_policies-spec-synopsis">Class
<code>const_item_policies</code> synopsis</a></dt>
<dt><a href="#const_item_policies-spec-statics">Class
<code>const_item_policies</code> static functions</a></dt>
</dl>
</dd>
<dt><a href="#item_policies-spec">Class
<code>item_policies</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#item_policies-spec-synopsis">Class
<code>item_policies</code> synopsis</a></dt>
<dt><a href="#item_policies-spec-statics">Class
<code>item_policies</code> static functions</a></dt>
</dl>
</dd>
<dt><a href="#const_slice_policies-spec">Class
<code>const_slice_policies</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#const_slice_policies-spec-synopsis">Class
<code>const_slice_policies</code> synopsis</a></dt>
<dt><a href="#const_slice_policies-spec-statics">Class
<code>const_slice_policies</code> static functions</a></dt>
</dl>
</dd>
<dt><a href="#slice_policies-spec">Class
<code>slice_policies</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#slice_policies-spec-synopsis">Class
<code>slice_policies</code> synopsis</a></dt>
<dt><a href="#slice_policies-spec-statics">Class
<code>slice_policies</code> static functions</a></dt>
</dl>
</dd>
<dt><a href="#object_operators-spec">Class
<code>object_operators</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#object_operators-spec-synopsis">Class
<code>object_operators</code> synopsis</a></dt>
<dt><a href="#object_operators-spec-observers">Class
<code>object_operators</code> observer functions</a></dt>
</dl>
</dd>
<dt><a href="#object-spec">Class <code>object</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#object-spec-synopsis">Class <code>object</code>
synopsis</a></dt>
<dt><a href="#object-spec-ctors">Class <code>object</code>
constructors and destructor</a></dt>
<dt><a href="#object-spec-modifiers">Class template
<code>object</code> modifier functions</a></dt>
<dt><a href="#object-spec-observers">Class template
<code>object</code> observer functions</a></dt>
</dl>
</dd>
<dt><a href="#proxy-spec">Class template
<code>proxy</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#proxy-spec-synopsis">Class template
<code>proxy</code> synopsis</a></dt>
<dt><a href="#proxy-spec-modifiers">Class template
<code>proxy</code> modifier functions</a></dt>
<dt><a href="#proxy-spec-observers">Class template
<code>proxy</code> observer functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#functions">Functions</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#del-spec">del</a></dt>
<dt><a href="#comparisons-spec">comparisons</a></dt>
<dt><a href="#binary-spec">binary operations</a></dt>
<dt><a href="#assignment-spec">assignment operations</a></dt>
</dl>
<dl class="page-index">
<dt><a href="#operators-spec">operators</a></dt>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>Exposes the generic Python object wrapper class <code>object</code>,
and related classes. In order to avoid some potenential problems with
argument-dependent lookup and the generalized operators defined on
<code>object</code>, all these facilities are defined in
<code>namespace&nbsp;boost::python::api</code>, and <code>object</code>
is imported into <code>namespace&nbsp;boost::python</code> with a
<i>using-declaration</i>.</p>
<h2><a name="types"></a>Types</h2>
<p><a name="slice_nil-spec"></a></p>
<pre>
enum slice_nil { _ };
</pre>
A type that can be used to get the effect of leaving out an index in a
Python slice expression:
<pre>
&gt;&gt;&gt; x[:-1]
</pre>
C++ equivalent:
<pre>
x.slice(_,-1)
</pre>
<h2><a name="classes"></a>Classes</h2>
<!-- begin -->
<h3><a name="const_attribute_policies-spec"></a>Class
<code>const_attribute_policies</code></h3>
<p>The policies which are used for proxies representing an attribute
access to a <code>const&nbsp;object</code>.</p>
<h4><a name="class-spec-synopsis"></a>Class
<code>const_attribute_policies</code> synopsis</h4>
<pre>
namespace boost { namespace python { namespace api
{
struct const_attribute_policies
{
typedef char const* key_type;
static object get(object const&amp; target, char const* key);
};
}}}
</pre>
<h4><a name="const_attribute_policies-spec-statics"></a>Class
<code>const_attribute_policies</code> static functions</h4>
<pre>
static object get(object const&amp; target, char const* key);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>key</code> is an <a href=
"definitions.html#ntbs">ntbs</a>.</dt>
<dt><b>Effects:</b> accesses the attribute of <code>target</code> named
by <code>key</code>.</dt>
<dt><b>Returns:</b> An <code>object</code> managing the result of the
attribute access.</dt>
<dt><b>Throws:</b> <code><a href=
"errors.html#error_already_set-spec">error_already_set</a></code> if a
Python exception is raised.</dt>
</dl>
<h3><a name="attribute_policies-spec"></a>Class
<code>attribute_policies</code></h3>
<p>The policies which are used for proxies representing an attribute
access to a mutable <code>object</code>.</p>
<h4><a name="attribute_policies-spec-synopsis"></a>Class
<code>attribute_policies</code> synopsis</h4>
<pre>
namespace boost { namespace python { namespace api
{
struct attribute_policies : const_attribute_policies
{
static object const&amp; set(object const&amp; target, char const* key, object const&amp; value);
static void del(object const&amp;target, char const* key);
};
}}}
</pre>
<h4><a name="attribute_policies-spec-statics"></a>Class
<code>attribute_policies</code> static functions</h4>
<pre>
static object const&amp; set(object const&amp; target, char const* key, object const&amp; value);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>key</code> is an <a href=
"definitions.html#ntbs">ntbs</a>.</dt>
<dt><b>Effects:</b> sets the attribute of <code>target</code> named by
<code>key</code> to <code>value</code>.</dt>
<dt><b>Throws:</b> <code><a href=
"errors.html#error_already_set-spec">error_already_set</a></code> if a
Python exception is raised.</dt>
</dl>
<pre>
static void del(object const&amp;target, char const* key);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>key</code> is an <a href=
"definitions.html#ntbs">ntbs</a>.</dt>
<dt><b>Effects:</b> deletes the attribute of <code>target</code> named
by <code>key</code>.</dt>
<dt><b>Throws:</b> <code><a href=
"errors.html#error_already_set-spec">error_already_set</a></code> if a
Python exception is raised.</dt>
</dl>
<!-- end -->
<!-- begin -->
<h3><a name="const_item_policies-spec"></a>Class
<code>const_item_policies</code></h3>
<p>The policies which are used for proxies representing an item access
(via the Python bracket operators <code>[]</code>) to a
<code>const&nbsp;object</code>.</p>
<h4><a name="const_item_policies-spec-synopsis"></a>Class
<code>const_item_policies</code> synopsis</h4>
<pre>
namespace boost { namespace python { namespace api
{
struct const_item_policies
{
typedef object key_type;
static object get(object const&amp; target, object const&amp; key);
};
}}}
</pre>
<h4><a name="const_item_policies-spec-statics"></a>Class
<code>const_item_policies</code> static functions</h4>
<pre>
static object get(object const&amp; target, object const&amp; key);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> accesses the item of <code>target</code> specified
by <code>key</code>.</dt>
<dt><b>Returns:</b> An <code>object</code> managing the result of the
item access.</dt>
<dt><b>Throws:</b> <code><a href=
"errors.html#error_already_set-spec">error_already_set</a></code> if a
Python exception is raised.</dt>
</dl>
<h3><a name="item_policies-spec"></a>Class
<code>item_policies</code></h3>
<p>The policies which are used for proxies representing an item access
(via the Python bracket operators <code>[]</code>) to a mutable
<code>object</code>.</p>
<h4><a name="item_policies-spec-synopsis"></a>Class
<code>item_policies</code> synopsis</h4>
<pre>
namespace boost { namespace python { namespace api
{
struct item_policies : const_item_policies
{
static object const&amp; set(object const&amp; target, object const&amp; key, object const&amp; value);
static void del(object const&amp; target, object const&amp; key);
};
}}}
</pre>
<h4><a name="item_policies-spec-statics"></a>Class
<code>item_policies</code> static functions</h4>
<pre>
static object const&amp; set(object const&amp; target, object const&amp; key, object const&amp; value);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> sets the item of <code>target</code> specified by
<code>key</code> to <code>value</code>.</dt>
<dt><b>Throws:</b> <code><a href=
"errors.html#error_already_set-spec">error_already_set</a></code> if a
Python exception is raised.</dt>
</dl>
<pre>
static void del(object const&amp; target, object const&amp; key);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> deletes the item of <code>target</code> specified
by <code>key</code>.</dt>
<dt><b>Throws:</b> <code><a href=
"errors.html#error_already_set-spec">error_already_set</a></code> if a
Python exception is raised.</dt>
</dl>
<!-- end -->
<!-- begin -->
<h3><a name="const_slice_policies-spec"></a>Class
<code>const_slice_policies</code></h3>
<p>The policies which are used for proxies representing an slice access
(via the Python slice notation
<code>[</code><i>x</i><code>:</code><i>y</i><code>]</code>) to a
<code>const&nbsp;object</code>.</p>
<h4><a name="const_slice_policies-spec-synopsis"></a>Class
<code>const_slice_policies</code> synopsis</h4>
<pre>
namespace boost { namespace python { namespace api
{
struct const_slice_policies
{
typedef std::pair&lt;handle&lt;&gt;, handle&lt;&gt; &gt; key_type;
static object get(object const&amp; target, key_type const&amp; key);
};
}}}
</pre>
<h4><a name="const_slice_policies-spec-statics"></a>Class
<code>const_slice_policies</code> static functions</h4>
<pre>
static object get(object const&amp; target, key_type const&amp; key);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> accesses the slice of <code>target</code> specified
by <code>key</code>.</dt>
<dt><b>Returns:</b> An <code>object</code> managing the result of the
slice access.</dt>
<dt><b>Throws:</b> <code><a href=
"errors.html#error_already_set-spec">error_already_set</a></code> if a
Python exception is raised.</dt>
</dl>
<h3><a name="slice_policies-spec"></a>Class
<code>slice_policies</code></h3>
<p>The policies which are used for proxies representing an slice access
to a mutable <code>object</code>.</p>
<h4><a name="slice_policies-spec-synopsis"></a>Class
<code>slice_policies</code> synopsis</h4>
<pre>
namespace boost { namespace python { namespace api
{
struct slice_policies : const_slice_policies
{
static object const&amp; set(object const&amp; target, key_type const&amp; key, object const&amp; value);
static void del(object const&amp; target, key_type const&amp; key);
};
}}}
</pre>
<h4><a name="slice_policies-spec-statics"></a>Class
<code>slice_policies</code> static functions</h4>
<pre>
static object const&amp; set(object const&amp; target, key_type const&amp; key, object const&amp; value);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> sets the slice of <code>target</code> specified by
<code>key</code> to <code>value</code>.</dt>
<dt><b>Throws:</b> <code><a href=
"errors.html#error_already_set-spec">error_already_set</a></code> if a
Python exception is raised.</dt>
</dl>
<pre>
static void del(object const&amp; target, key_type const&amp; key);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> deletes the slice of <code>target</code> specified
by <code>key</code>.</dt>
<dt><b>Throws:</b> <code><a href=
"errors.html#error_already_set-spec">error_already_set</a></code> if a
Python exception is raised.</dt>
</dl>
<!-- end -->
<h3><a name="object_operators-spec"></a>Class template
<code>object_operators&lt;U&gt;</code></h3>
<p>This is the base class of <code>object</code> and its
<code>proxy</code> template used to supply common interface: member
functions, and operators which must be defined within the class body. Its
template parameter <code>U</code> is expected to be a class derived from
<code>object_operators&lt;U&gt;</code>. In practice users should never
use this class directly, but it is documented here because it supplies
important interface to <code>object</code> and its proxies.</p>
<h4><a name="object_operators-spec-synopsis"></a>Class template
<code>object_operators</code> synopsis</h4>
<pre>
namespace boost { namespace python { namespace api
{
template &lt;class U&gt;
class object_operators
{
public:
// function call
//
object operator()() const;
template &lt;class A0&gt;
object operator()(A0 const&amp;) const;
template &lt;class A0, class A1&gt;
object operator()(A0 const&amp;, A1 const&amp;) const;
...
template &lt;class A0, class A1,...class An&gt;
object operator()(A0 const&amp;, A1 const&amp;,...An const&amp;) const;
// truth value testing
//
typedef unspecified bool_type;
operator bool_type() const;
// Attribute access
//
proxy&lt;const_object_attribute&gt; attr(char const*) const;
proxy&lt;object_attribute&gt; attr(char const*);
// item access
//
template &lt;class T&gt;
proxy&lt;const_object_item&gt; operator[](T const&amp; key) const;
template &lt;class T&gt;
proxy&lt;object_item&gt; operator[](T const&amp; key);
// slicing
//
template &lt;class T, class V&gt;
proxy&lt;const_object_slice&gt; slice(T const&amp; start, V const&amp; end) const
template &lt;class T, class V&gt;
proxy&lt;object_slice&gt; slice(T const&amp; start, V const&amp; end);
};
}}}
</pre>
<h4><a name="object_operators-spec-observers"></a>Class template
<code>object_operators</code> observer functions</h4>
<pre>
object operator()() const;
template &lt;class A0&gt;
object operator()(A0 const&amp;) const;
template &lt;class A0, class A1&gt;
object operator()(A0 const&amp;, A1 const&amp;) const;
...
template &lt;class A0, class A1,...class An&gt;
object operator()(A0 const&amp; a1, A1 const&amp; a2,...An const&amp; aN) const;
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
call&lt;object&gt;(object(*static_cast&lt;U*&gt;(this)).ptr(), a1,
a2,...aN)</dt>
</dl>
<pre>
operator bool_type() const;
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> Tests truth value of <code>*this</code>.</dt>
<dt><b>Returns:</b>
call&lt;object&gt;(object(*static_cast&lt;U*&gt;(this)).ptr(), a1,
a2,...aN)</dt>
</dl>
<pre>
proxy&lt;const_object_attribute&gt; attr(char const* name) const;
proxy&lt;object_attribute&gt; attr(char const* name);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> name is an <a href=
"definitions.html#ntbs">ntbs</a>.</dt>
<dt><b>Effects:</b> accesses the named attribute of
<code>*this</code>.</dt>
<dt><b>Returns:</b> a proxy object which binds
<code>object(*static_cast&lt;U*&gt;(this))</code> as its target, and
<code>name</code> as its key.</dt>
</dl>
<pre>
template &lt;class T&gt;
proxy&lt;const_object_item&gt; operator[](T const&amp; key) const;
template &lt;class T&gt;
proxy&lt;object_item&gt; operator[](T const&amp; key);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> accesses the item of <code>*this</code> indicated
by <code>key</code>.</dt>
<dt><b>Returns:</b> a proxy object which binds
<code>object(*static_cast&lt;U*&gt;(this))</code> as its target, and
<code>object(key)</code> as its key.</dt>
</dl>
<pre>
template &lt;class T, class V&gt;
proxy&lt;const_object_slice&gt; slice(T const&amp; start; start, V const&amp; finish) const
template &lt;class T, class V&gt;
proxy&lt;object_slice&gt; slice(T const&amp; start; start, V const&amp; finish);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> accesses the slice of <code>*this</code> indicated
by <code>std::make_pair(object(start), object(finish))</code>.</dt>
<dt><b>Returns:</b> a proxy object which binds
<code>object(*static_cast&lt;U*&gt;(this))</code> as its target, and
<code>std::make_pair(object(start), object(finish))</code> as its
key.</dt>
</dl>
<!-- -->
<h3><a name="object-spec"></a>Class <code>object</code></h3>
<p>The intention is that <code>object</code> acts as much like a
Python variable as possible. Thus expressions you'd expect to work
in Python should generally work in the same way from C++. Most of
<code>object</code>'s interface is provided by its base class
<code><a
href="#object_operators-spec">object_operators</a>&lt;object&gt;</code>,
and the <a href="#functions">free functions</a> defined in this
header.
</p>
<h4><a name="object-spec-synopsis"></a>Class <code>object</code>
synopsis</h4>
<pre>
namespace boost { namespace python { namespace api
{
class object : public object_operators&lt;object&gt;
{
public:
object();
object(object const&amp;);
template &lt;class T&gt;
explicit object(T const&amp; x);
~object();
object&amp; operator=(object const&amp;);
PyObject* ptr() const;
};
}}}
</pre>
<h4><a name="object-spec-ctors"></a>Class <code>object</code>
constructors and destructor</h4>
<pre>
object();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> Constructs an object managing a reference to the
Python <code>None</code> object.</dt>
<dt><b>Throws:</b> nothing.</dt>
</dl>
<pre>
template &lt;class T&gt;
explicit object(T const&amp; x);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> converts <code>x</code> to python and manages a
reference to it.</dt>
<dt><b>Throws:</b> <code>error_already_set</code> and sets a Python
<code>TypeError</code> exception if no such conversion is
possible.</dt>
</dl>
<pre>
~object();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> decrements the reference count of the
internally-held object.</dt>
</dl>
<h4><a name="object-spec-modifiers"></a>Class <code>object</code>
modifiers</h4>
<pre>
object&amp; operator=(object const&amp; rhs);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> increments the reference count of the object held
by <code>rhs</code> and decrements the reference count of the object
held by <code>*this</code>.</dt>
</dl>
<h4><a name="object-spec-observers"></a>Class <code>object</code>
observers</h4>
<pre>
PyObject* ptr() const;
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> a pointer to the internally-held Python
object.</dt>
</dl>
<!-- -->
<h3><a name="proxy-spec"></a>Class template <code>proxy</code></h3>
<p>This template is instantiated with various Policies described in this
document in order to implement attribute, item, and slice access for
<code>object</code>. It stores an object of type
<code>Policies::key_type</code>.</p>
<h4><a name="proxy-spec-synopsis"></a>Class template <code>proxy</code>
synopsis</h4>
<pre>
namespace boost { namespace python { namespace api
{
template &lt;class Policies&gt;
class proxy : public object_operators&lt;proxy&lt;Policies&gt; &gt;
{
public:
operator object() const;
proxy const&amp; operator=(proxy const&amp;) const;
template &lt;class T&gt;
inline proxy const&amp; operator=(T const&amp; rhs) const;
void del() const;
template &lt;class R&gt;
proxy operator+=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator-=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator*=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator/=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator%=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator&lt;&lt;=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator&gt;&gt;=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator&amp;=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator|=(R const&amp; rhs);
};
}}}
</pre>
<h4><a name="proxy-spec-observers"></a>Class template <code>proxy</code>
observer functions</h4>
<pre>
operator object() const;
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> applies
<code>Policies::get(</code><i>target</i><code>,</code>&nbsp;<i>key</i>
<code>)</code> with the proxy's target and key objects.</dt>
</dl>
<h4><a name="proxy-spec-modifiers"></a>Class template <code>proxy</code>
modifier functions</h4>
<pre>
proxy const&amp; operator=(proxy const&amp; rhs) const;
template &lt;class T&gt;
inline proxy const&amp; operator=(T const&amp; rhs) const;
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>Policies::set(</code><i>target</i><code>,</code>&nbsp;<i>key</i>
<code>,&nbsp;object(rhs))</code> with the proxy's target and key
objects.</dt>
</dl>
<pre>
template &lt;class R&gt;
proxy operator+=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator-=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator*=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator/=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator%=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator&lt;&lt;=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator&gt;&gt;=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator&amp;=(R const&amp; rhs);
template &lt;class R&gt;
proxy operator|=(R const&amp; rhs);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> for a given operator@=,
<code>object(*this)&nbsp;@=&nbsp;rhs;</code></dt>
<dt><b>Returns:</b> <code>*this</code></dt>
</dl>
<pre>
void del() const;
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b>
<code>Policies::del(</code><i>target</i><code>,</code>&nbsp;<i>key</i>
<code>)</code> with the proxy's target and key objects.</dt>
</dl>
<!-- -->
<h2><a name="functions"></a>Functions</h2>
<pre>
<a name="del-spec"></a>template &lt;class T&gt;
void del(proxy&lt;T&gt; const&amp; x);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> x.del()</dt>
</dl>
<pre>
<a name="comparisons-spec"></a>
template&lt;class L,class R&gt; bool operator&gt;(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; bool operator&gt;=(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; bool operator&lt;(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; bool operator&lt;=(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; bool operator==(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; bool operator!=(L const&amp;l,R const&amp;r);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> returns the result of applying the operator to
<code>object(l)</code> and <code>object(r)</code>, respectively, in
Python.</dt>
</dl>
<pre>
<a name="binary-spec"></a>
template&lt;class L,class R&gt; object operator+(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; object operator-(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; object operator*(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; object operator/(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; object operator%(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; object operator&lt;&lt;(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; object operator&gt;&gt;(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; object operator&amp;(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; object operator^(L const&amp;l,R const&amp;r);
template&lt;class L,class R&gt; object operator|(L const&amp;l,R const&amp;r);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> returns the result of applying the operator to
<code>object(l)</code> and <code>object(r)</code>, respectively, in
Python.</dt>
</dl>
<pre>
<a name="assignment-spec"></a>
template&lt;class R&gt; object&amp; operator+=(object&amp;l,R const&amp;r);
template&lt;class R&gt; object&amp; operator-=(object&amp;l,R const&amp;r);
template&lt;class R&gt; object&amp; operator*=(object&amp;l,R const&amp;r);
template&lt;class R&gt; object&amp; operator/=(object&amp;l,R const&amp;r);
template&lt;class R&gt; object&amp; operator%=(object&amp;l,R const&amp;r);
template&lt;class R&gt; object&amp; operator&lt;&lt;=(object&amp;l,R const&amp;r)
template&lt;class R&gt; object&amp; operator&gt;&gt;=(object&amp;l,R const&amp;r);
template&lt;class R&gt; object&amp; operator&amp;=(object&amp;l,R const&amp;r);
template&lt;class R&gt; object&amp; operator^=(object&amp;l,R const&amp;r);
template&lt;class R&gt; object&amp; operator|=(object&amp;l,R const&amp;r);
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> assigns to l the result of applying the
corresponding Python inplace operator to <code>l</code> and
<code>object(r)</code>, respectively.</dt>
<dt><b>Returns:</b> <code>l</code>.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
Python code:
<pre>
def sum_items(seq):
result = 0
for x in seq:
result += x
return result
</pre>
C++ version:
<pre>
object sum_items(object seq)
{
object result = object(0);
for (int i = 0; i &lt; seq.attr("__len__")(); ++i)
result += seq[i];
return result;
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
02 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/operators.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#self_t-spec">Class
<code>self_ns::self_t</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#self_t-spec-synopsis">Class <code>self_t</code>
synopsis</a></dt>
<dt><a href="#self_t-spec-inplace">Class <code>self_t</code>
inplace operators</a></dt>
<dt><a href="#self_t-spec-comparisons">Class
<code>self_t</code> comparison functions</a></dt>
<dt><a href="#self_t-spec-ops">Class <code>self_t</code>
non-member operations</a></dt>
<dt><a href="#self_t-spec-value-unary-ops">Class
<code>self_t</code> unary operations</a></dt>
<dt><a href="#self_t-spec-value-value-ops">Class
<code>self_t</code> value operations</a></dt>
</dl>
</dd>
<dt><a href="#other-spec">Class template
<code>other</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#other-spec-synopsis">Class <code>other</code>
synopsis</a></dt>
</dl>
</dd>
<dt><a href="#operator_-spec">Class template
<code>operator_</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#operator_-spec-synopsis">Class
<code>operator_</code> synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#objects">Objects</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#self-spec">self</a></dt>
</dl>
</dd>
<dt><a href="#examples">Examples</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/operators.hpp&gt;</code> provides types and
functions for automatically generating Python <a href=
"http://www.python.org/doc/ref/specialnames.html">special methods</a>
from the corresponding C++ constructs. Most of these constructs are
operator expressions, hence the name. To use the facility, substitute the
<code><a href="#self-spec">self</a></code> object for an object of the
class type being wrapped in the expression to be exposed, and pass the
result to <a href=
"class.html#class_-spec-modifiers">class_&lt;&gt;::def()</a>. Much of
what is exposed in this header should be considered part of the
implementation, so is not documented in detail here.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="self_t-spec"></a>Class <code>self_ns::self_t</code></h3>
<p><code>self_ns::self_t</code> is the actual type of the <a href=
"#self-spec"><code>self</code></a> object. The library isolates
<code>self_t</code> in its own namespace, <code>self_ns</code>, in order
to prevent the generalized operator templates which operate on it from
being found by argument-dependent lookup in other contexts. This should
be considered an implementation detail, since users should never have to
mention <code>self_t</code> directly.</p>
<h4><a name="self_t-spec-synopsis"></a>Class <code>self_ns::self_t</code>
synopsis</h4>
<pre>
namespace boost { namespace python { namespace self_ns {
{
<i>unspecified-type-declaration</i> self_t;
// inplace operators
template &lt;class T&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator+=(self_t, T);
template &lt;class T&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator-=(self_t, T);
template &lt;class T&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator*=(self_t, T);
template &lt;class T&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator/=(self_t, T);
template &lt;class T&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator%=(self_t, T);
template &lt;class T&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator&gt;&gt;=(self_t, T);
template &lt;class T&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator&lt;&lt;=(self_t, T);
template &lt;class T&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator&amp;=(self_t, T);
template &lt;class T&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator^=(self_t, T);
template &lt;class T&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator|=(self_t, T);
// comparisons
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator==(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator!=(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator&lt;(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator&gt;(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator&lt;=(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator&gt;=(L const&amp;, R const&amp;);
// non-member operations
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator+(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator-(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator*(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator/(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator%(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator&gt;&gt;(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator&lt;&lt;(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator&amp;(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator^(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator|(L const&amp;, R const&amp;);
template &lt;class L, class R&gt; <a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; pow(L const&amp;, R const&amp;);
// unary operations
<a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator-(self_t);
<a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator+(self_t);
<a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; operator~(self_t);
// value operations
<a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; int_(self_t);
<a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; long_(self_t);
<a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; float_(self_t);
<a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; complex_(self_t);
<a href=
"#operator_-spec">operator_</a>&lt;<i>unspecified</i>&gt; str(self_t);
}}};
</pre>
The tables below describe the methods generated when the results of the
expressions described are passed as arguments to <a href=
"class.html#class_-spec-modifiers">class_&lt;&gt;::def()</a>.
<code><b>x</b></code> is an object of the class type being wrapped.
<h4><a name="self_t-spec-inplace"></a>Class <code>self_t</code> inplace
operators</h4>
In the table below, If <code><b>r</b></code> is an object of type
<code><a href="#other-spec">other</a>&lt;T&gt;</code>,
<code><b>y</b></code> is an object of type <code>T</code>; otherwise,
<code><b>y</b></code> is an object of the same type as
<code><b>r</b></code>.
<table border="1" summary="self_t inplace operators">
<tr>
<th>C++ Expression</th>
<th>Python Method Name</th>
<th>C++ Implementation</th>
</tr>
<tr>
<td><code>self&nbsp;+=&nbsp;r</code></td>
<td><code>__iadd__</code></td>
<td><code>x&nbsp;+=&nbsp;y</code></td>
</tr>
<tr>
<td><code>self&nbsp;-=&nbsp;r</code></td>
<td><code>__isub__</code></td>
<td><code>x&nbsp;-=&nbsp;y</code></td>
</tr>
<tr>
<td><code>self&nbsp;*=&nbsp;r</code></td>
<td><code>__imul__</code></td>
<td><code>x&nbsp;*=&nbsp;y</code></td>
</tr>
<tr>
<td><code>self&nbsp;/=&nbsp;r</code></td>
<td><code>__idiv__</code></td>
<td><code>x&nbsp;/=&nbsp;y</code></td>
</tr>
<tr>
<td><code>self&nbsp;%=&nbsp;r</code></td>
<td><code>__imod__</code></td>
<td><code>x&nbsp;%=&nbsp;y</code></td>
</tr>
<tr>
<td><code>self&nbsp;&gt;&gt;=&nbsp;r</code></td>
<td><code>__irshift__</code></td>
<td><code>x&nbsp;&gt;&gt;=&nbsp;y</code></td>
</tr>
<tr>
<td><code>self&nbsp;&lt;&lt;=&nbsp;r</code></td>
<td><code>__ilshift__</code></td>
<td><code>x&nbsp;&lt;&lt;=&nbsp;y</code></td>
</tr>
<tr>
<td><code>self&nbsp;&amp;=&nbsp;r</code></td>
<td><code>__iand__</code></td>
<td><code>x&nbsp;&amp;=&nbsp;y</code></td>
</tr>
<tr>
<td><code>self&nbsp;^=&nbsp;r</code></td>
<td><code>__ixor__</code></td>
<td><code>x&nbsp;^=&nbsp;y</code></td>
</tr>
<tr>
<td><code>self&nbsp;|=&nbsp;r</code></td>
<td><code>__ior__</code></td>
<td><code>x&nbsp;|=&nbsp;y</code></td>
</tr>
</table>
<h4><a name="self_t-spec-comparisons"></a>Class <code>self_t</code>
comparison functions</h4>
In the tables below, if <code><b>r</b></code> is of type <code><a href=
"#self_t-spec">self_t</a></code>, <code><b>y</b></code> is an object of
the same type as <code>x</code>; <br>
if <code><b>l</b></code> or <code><b>r</b></code> is an object of type
<code><a href="#other-spec">other</a>&lt;T&gt;</code>,
<code><b>y</b></code> is an object of type <code>T</code>; <br>
otherwise, <code><b>y</b></code> is an object of the same type as
<code><b>l</b></code> or <code><b>r</b></code>.<br>
<code><b>l</b></code> is never of type <code><a href=
"#self_t-spec">self_t</a></code>.
<p>The column of <b>Python Expressions</b> illustrates the expressions
that will be supported in Python for objects convertible to the types of
<code>x</code> and <code>y</code>. The secondary operation arises due to
Python's <a href=
"http://www.python.org/doc/ref/customization.html#l2h-89">reflection
rules</a> for rich comparison operators, and are only used when the
corresponding operation is not defined as a method of the <code>y</code>
object.</p>
<table border="1" summary="self_t comparison functions">
<tr>
<th>C++ Expression</th>
<th>Python Method Name</th>
<th>C++ Implementation</th>
<th>Python Expressions<br>
(primary, secondary)</th>
</tr>
<tr>
<td>self&nbsp;==&nbsp;r</td>
<td>__eq__</td>
<td>x&nbsp;==&nbsp;y</td>
<td>x&nbsp;==&nbsp;y, y&nbsp;==&nbsp;x</td>
</tr>
<tr>
<td>l&nbsp;==&nbsp;self</td>
<td>__eq__</td>
<td>y&nbsp;==&nbsp;x</td>
<td>y&nbsp;==&nbsp;x, x&nbsp;==&nbsp;y</td>
</tr>
<tr>
<td>self&nbsp;!=&nbsp;r</td>
<td>__ne__</td>
<td>x&nbsp;!=&nbsp;y</td>
<td>x&nbsp;!=&nbsp;y, y&nbsp;!=&nbsp;x</td>
</tr>
<tr>
<td>l&nbsp;!=&nbsp;self</td>
<td>__ne__</td>
<td>y&nbsp;!=&nbsp;x</td>
<td>y&nbsp;!=&nbsp;x, x&nbsp;!=&nbsp;y</td>
</tr>
<tr>
<td>self&nbsp;&lt;&nbsp;r</td>
<td>__lt__</td>
<td>x&nbsp;&lt;&nbsp;y</td>
<td>x&nbsp;&lt;&nbsp;y, y&nbsp;&gt;&nbsp;x</td>
</tr>
<tr>
<td>l&nbsp;&lt;&nbsp;self</td>
<td>__gt__</td>
<td>y&nbsp;&lt;&nbsp;x</td>
<td>y&nbsp;&gt;&nbsp;x, x&nbsp;&lt;&nbsp;y</td>
</tr>
<tr>
<td>self&nbsp;&gt;&nbsp;r</td>
<td>__gt__</td>
<td>x&nbsp;&gt;&nbsp;y</td>
<td>x&nbsp;&gt;&nbsp;y, y&nbsp;&lt;&nbsp;x</td>
</tr>
<tr>
<td>l&nbsp;&gt;&nbsp;self</td>
<td>__lt__</td>
<td>y&nbsp;&gt;&nbsp;x</td>
<td>y&nbsp;&lt;&nbsp;x, x&nbsp;&gt;&nbsp;y</td>
</tr>
<tr>
<td>self&nbsp;&lt;=&nbsp;r</td>
<td>__le__</td>
<td>x&nbsp;&lt;=&nbsp;y</td>
<td>x&nbsp;&lt;=&nbsp;y, y&nbsp;&gt;=&nbsp;x</td>
</tr>
<tr>
<td>l&nbsp;&lt;=&nbsp;self</td>
<td>__ge__</td>
<td>y&nbsp;&lt;=&nbsp;x</td>
<td>y&nbsp;&gt;=&nbsp;x, x&nbsp;&lt;=&nbsp;y</td>
</tr>
<tr>
<td>self&nbsp;&gt;=&nbsp;r</td>
<td>__ge__</td>
<td>x&nbsp;&gt;=&nbsp;y</td>
<td>x&nbsp;&gt;=&nbsp;y, y&nbsp;&lt;=&nbsp;x</td>
</tr>
<tr>
<td>l&nbsp;&gt;=&nbsp;self</td>
<td>__le__</td>
<td>y&nbsp;&gt;=&nbsp;x</td>
<td>y&nbsp;&lt;=&nbsp;x, x&nbsp;&gt;=&nbsp;y</td>
</tr>
</table>
<h4><a name="self_t-spec-ops"></a>Class <code>self_t</code> non-member
operations</h4>
The operations whose names begin with "<code>__r</code>" below will only
be called if the left-hand operand does not already support the given
operation, as described <a href=
"http://www.python.org/doc/current/ref/numeric-types.html#l2h-152">here</a>.
<table border="1" summary="self_t non-member operations">
<tr>
<th>C++ Expression</th>
<th>Python Method Name</th>
<th>C++ Implementation</th>
</tr>
<tr>
<td>self&nbsp;+&nbsp;r</td>
<td>__add__</td>
<td>x&nbsp;+&nbsp;y</td>
</tr>
<tr>
<td>l&nbsp;+&nbsp;self</td>
<td>__radd__</td>
<td>y&nbsp;+&nbsp;x</td>
</tr>
<tr>
<td>self&nbsp;-&nbsp;r</td>
<td>__sub__</td>
<td>x&nbsp;-&nbsp;y</td>
</tr>
<tr>
<td>l&nbsp;-&nbsp;self</td>
<td>__rsub__</td>
<td>y&nbsp;-&nbsp;x</td>
</tr>
<tr>
<td>self&nbsp;*&nbsp;r</td>
<td>__mul__</td>
<td>x&nbsp;*&nbsp;y</td>
</tr>
<tr>
<td>l&nbsp;*&nbsp;self</td>
<td>__rmul__</td>
<td>y&nbsp;*&nbsp;x</td>
</tr>
<tr>
<td>self&nbsp;/&nbsp;r</td>
<td>__div__</td>
<td>x&nbsp;/&nbsp;y</td>
</tr>
<tr>
<td>l&nbsp;/&nbsp;self</td>
<td>__rdiv__</td>
<td>y&nbsp;/&nbsp;x</td>
</tr>
<tr>
<td>self&nbsp;%&nbsp;r</td>
<td>__mod__</td>
<td>x&nbsp;%&nbsp;y</td>
</tr>
<tr>
<td>l&nbsp;%&nbsp;self</td>
<td>__rmod__</td>
<td>y&nbsp;%&nbsp;x</td>
</tr>
<tr>
<td>self&nbsp;&gt;&gt;&nbsp;r</td>
<td>__rshift__</td>
<td>x&nbsp;&gt;&gt;&nbsp;y</td>
</tr>
<tr>
<td>l&nbsp;&gt;&gt;&nbsp;self</td>
<td>__rrshift__</td>
<td>y&nbsp;&gt;&gt;&nbsp;x</td>
</tr>
<tr>
<td>self&nbsp;&lt;&lt;&nbsp;r</td>
<td>__lshift__</td>
<td>x&nbsp;&lt;&lt;&nbsp;y</td>
</tr>
<tr>
<td>l&nbsp;&lt;&lt;&nbsp;self</td>
<td>__rlshift__</td>
<td>y&nbsp;&lt;&lt;&nbsp;x</td>
</tr>
<tr>
<td>self&nbsp;&amp;&nbsp;r</td>
<td>__and__</td>
<td>x&nbsp;&amp;&nbsp;y</td>
</tr>
<tr>
<td>l&nbsp;&amp;&nbsp;self</td>
<td>__rand__</td>
<td>y&nbsp;&amp;&nbsp;x</td>
</tr>
<tr>
<td>self&nbsp;^&nbsp;r</td>
<td>__xor__</td>
<td>x&nbsp;^&nbsp;y</td>
</tr>
<tr>
<td>l&nbsp;^&nbsp;self</td>
<td>__rxor__</td>
<td>y&nbsp;^&nbsp;x</td>
</tr>
<tr>
<td>self&nbsp;|&nbsp;r</td>
<td>__or__</td>
<td>x&nbsp;|&nbsp;y</td>
</tr>
<tr>
<td>l&nbsp;|&nbsp;self</td>
<td>__ror__</td>
<td>y&nbsp;|&nbsp;x</td>
</tr>
<tr>
<td>pow(self,&nbsp;r)</td>
<td>__pow__</td>
<td>pow(x,&nbsp;y)</td>
</tr>
<tr>
<td>pow(l,&nbsp;self)</td>
<td>__rpow__</td>
<td>pow(y,&nbsp;x)</td>
</tr>
</table>
<h4><a name="self_t-spec-unary-ops"></a>Class <code>self_t</code> unary
operations</h4>
<table border="1" summary="self_t unary operations">
<tr>
<th>C++ Expression</th>
<th>Python Method Name</th>
<th>C++ Implementation</th>
</tr>
<tr>
<td>-self</td>
<td>__neg__</td>
<td>-x</td>
</tr>
<tr>
<td>+self</td>
<td>__pos__</td>
<td>+x</td>
</tr>
<tr>
<td>~self</td>
<td>__invert__</td>
<td>~x</td>
</tr>
</table>
<h4><a name="self_t-spec-value-ops"></a>Class <code>self_t</code> value
operations</h4>
<table border="1" summary="self_t value operations">
<tr>
<th>C++ Expression</th>
<th>Python Method Name</th>
<th>C++ Implementation</th>
</tr>
<tr>
<td>int_(self)</td>
<td>__int__</td>
<td>long(x)</td>
</tr>
<tr>
<td>long_</td>
<td>__long__</td>
<td>PyLong_FromLong(x)</td>
</tr>
<tr>
<td>float_</td>
<td>__float__</td>
<td>double(x)</td>
</tr>
<tr>
<td>complex_</td>
<td>__complex__</td>
<td>std::complex&lt;double&gt;(x)</td>
</tr>
<tr>
<td>str</td>
<td>__str__</td>
<td><a href=
"../../../conversion/lexical_cast.htm#lexical_cast">lexical_cast</a>&lt;std::string&gt;(x)</td>
</tr>
</table>
<h3><a name="other-spec"></a>Class Template <code>other</code></h3>
<p>Instances of <code>other&lt;T&gt;</code> can be used in operator
expressions with <a href="#self-spec">self</a>; the result is equivalent
to the same expression with a <code>T</code> object in place of
<code>other&lt;T&gt;</code>. Use <code>other&lt;T&gt;</code> to prevent
construction of a <code>T</code> object in case it is heavyweight, when
no constructor is available, or simply for clarity.</p>
<h4><a name="other-spec-synopsis"></a>Class Template other synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class T&gt;
struct other
{
};
}}
</pre>
<!-- -->
<h3><a name="operator_-spec"></a>Class Template
<code>detail::operator_</code></h3>
<p>Instantiations of <code>detail::operator_&lt;&gt;</code> are used as
the return type of operator expressions involving <code><a href=
"#self-spec">self</a></code>. This should be considered an implementation
detail and is only documented here as a way of showing how the result of
<code>self</code>-expressions match calls to <a href=
"class.html#class_-spec-modifiers">class_&lt;&gt;::def()</a>.</p>
<h4><a name="operator_-spec-synopsis"></a>Class Template
<code>detail::operator_</code> synopsis</h4>
<pre>
namespace boost { namespace python { namespace detail
{
template &lt;<i>unspecified</i>&gt;
struct operator_
{
};
}}}
</pre>
<h2><a name="objects"></a>Objects</h2>
<p><a name="self-spec"><code>self</code></a></p>
<pre>
namespace boost { namespace python
{
using self_ns::self;
}}
</pre>
<h2><a name="examples"></a>Example</h2>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/operators.hpp&gt;
#include &lt;boost/operators.hpp&gt;
struct number
: boost::<a href=
"../../../utility/operators.htm#grpd_oprs">integer_arithmetic</a>&lt;number&gt;
{
number(long x_) : x(x_) {}
operator long() const { return x; }
number&amp; operator+=(number const&amp; rhs)
{ x += rhs }
number&amp; operator-=(number const&amp; rhs);
{ x -= rhs }
number&amp; operator*=(number const&amp; rhs)
{ x *= rhs }
number&amp; operator/=(number const&amp; rhs);
{ x /= rhs }
number&amp; operator%=(number const&amp; rhs);
{ x %= rhs }
long x;
};
using namespace boost::python;
BOOST_PYTHON_MODULE(demo)
{
class_&lt;number&gt;("number")
// interoperate with self
.def(self += self)
.def(self + self)
.def(self -= self)
.def(self - self)
.def(self *= self)
.def(self * self)
.def(self /= self)
.def(self / self)
.def(self %= self)
.def(self % self)
// Convert to Python int
.def(int_(self))
// interoperate with long
.def(self += long())
.def(self + long())
.def(long() + self)
.def(self -= long())
.def(self - long())
.def(long() - self)
.def(self *= long())
.def(self * long())
.def(long() * self)
.def(self /= long())
.def(self / long())
.def(long() / self)
.def(self %= long())
.def(self % long())
.def(long() % self)
;
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 Sept, 2002 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<title>Boost.Python - &lt;boost/python/overloads.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
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<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/overloads.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href=
"#overload-dispatch-expression"><i>overload-dispatch-expressions</i></a></dt>
<dt><a href= "#OverloadDispatcher-concept">OverloadDispatcher</a> concept</dt>
<dt><a href="#macros">Macros</a></dt>
<dd>
<dl class="page-index">
<dt><a href=
"#BOOST_PYTHON_FUNCTION_OVERLOADS-spec">BOOST_PYTHON_FUNCTION_OVERLOADS</a></dt>
<dt><a href=
"#BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS-spec">BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS</a></dt>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>Defines facilities for generating families of overloaded Python
functions and extension class methods from C++ functions and
member functions with default arguments, or from similar families
of C++ overloads</p>
<h2><a name=
"overload-dispatch-expression"></a><i>overload-dispatch-expressions</i></h2>
<p>
An <em>overload-dispatch-expression</em> is used to describe a
family of overloaded methods to be generated for an extension
class. It has the following properties:
<blockquote>
<dl class="properties">
<dt><b>docstring:</b> An <a href="definitions.html#ntbs">ntbs</a>
whose value will bound to the methods' <code>__doc__</code>
attribute</dt>
<dt><b>keywords:</b> A <a href=
"args.html#keyword-expression">keyword-expression</a> which
will be used to name (a trailing subsequence of) the arguments
to the generated methods.</dt>
<dt><b>call policies:</b> An instance of some type which models <a href=
"CallPolicies.html">CallPolicies</a>.</dt>
<dt><b>minimum <a href="definitions.html#arity">arity</a></b>
The minimum number of arguments to be accepted by a generated
method overload.</dt>
<dt><b>maximum <a href="definitions.html#arity">arity</a></b>
The maximum number of arguments to be accepted by a generated
method overload.</dt>
</dl>
</blockquote>
<h2><a name="OverloadDispatcher-concept"></a>OverloadDispatcher Concept</h2>
An OverloadDispatcher <code>X</code> is a class which has a
<em>minimum arity</em> and a <em>maximum arity</em>, and for which
the following following are valid <a
href="#overload-dispatch-expression"><em>overload-dispatch-expression</em></a>s,
with the same minimum and maximum arity as the OverloadDispatcher.
<pre>
X()
X(docstring)
X(docstring, keywords)
X(keywords, docstring)
X()[policies]
X(docstring)[policies]
X(docstring, keywords)[policies]
X(keywords, docstring)[policies]
</pre>
<ul>
<li>If <code>policies</code> are supplied, it must be an instance of a
type which models <a
href="CallPolicies.html#CallPolicies-concept">CallPolicies</a>, and
will be used as the result's call policies. Otherwise the result's
call policies will be an instance of <a
href="default_call_policies.html#default_call_policies-spec">default_call_policies</a>.
<li>If <code>docstring</code> is supplied it must be an <a
href="definitions.html#ntbs">ntbs</a>, and will be used as the result's docstring. Otherwise the result has an empty docstring.
<li>If <code>keywords</code> is supplied it must be the result of a <a
href= "args.html#keyword-expression">keyword-expression</a>
whose length is no greater than <code>X</code>'s maximum
arity, and will be used as the result's keywords. Otherwise
the result's keywords will be empty.
</ul>
<h2><a name="macros"></a>Macros</h2>
<h3><a name=
"BOOST_PYTHON_FUNCTION_OVERLOADS-spec">BOOST_PYTHON_FUNCTION_OVERLOADS(name,&nbsp;func_id,&nbsp;min_args,&nbsp;max_args)</a></h3>
Expands to the definition of an OverloadDispatcher called
<code>name</code> in the current scope which can be used to
generate the following function invocation:
<pre>
func_id(a<small><i>1</i></small>, a<small><i>2</i></small>,...a<small><i>i</i></small>);
</pre>
for all <code>min_args</code> &lt;= <i>i</i> &lt;= <code>max_args</code>.
<h3><a name=
"BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS-spec">BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(name,&nbsp;member_name,&nbsp;min_args,&nbsp;max_args)</a></h3>
Expands to the definition of an OverloadDispatcher called
<code>name</code> in the current scope which can be used to
generate the following function invocation:
<pre>
x.member_name(a<small><i>1</i></small>, a<small><i>2</i></small>,...a<small><i>i</i></small>);
</pre>
for all <code>min_args</code> &lt;= <i>i</i> &lt;=
<code>max_args</code>, where <code>x</code> is a reference to an
object of class type.
<h2><a name="examples"></a>Example(s)</h2>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/def.hpp&gt;
#include &lt;boost/python/args.hpp&gt;
#include &lt;boost/python/tuple.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/overloads.hpp&gt;
#include &lt;boost/python/return_internal_reference.hpp&gt;
using namespace boost::python;
tuple f(int x = 1, double y = 4.25, char const* z = &quot;wow&quot;)
{
return make_tuple(x, y, z);
}
BOOST_PYTHON_FUNCTION_OVERLOADS(f_overloads, f, 0, 3)
stryct Y {};
struct X
{
Y&amp; f(int x, double y = 4.25, char const* z = &quot;wow&quot;)
{
return inner;
}
Y inner;
};
BOOST_PYTHON_MEMBER_FUNCTION_OVERLOADS(X_f_overloads, X::f, 1, 3)
BOOST_PYTHON_MODULE(args_ext)
{
def(&quot;f&quot;, f, args(&quot;x&quot;, &quot;y&quot;, &quot;z&quot;)
, &quot;This is f's docstring&quot;
);
class_&lt;Y&gt;(&quot;Y&quot;)
;
class_&lt;X&gt;(&quot;X&quot;, &quot;This is X's docstring&quot;)
.def(&quot;f1&quot;, &amp;X::f,
X_f_overloads(args(&quot;x&quot;, &quot;y&quot;, &quot;z&quot;),
&quot;f's docstring&quot;
)[return_internal_reference&lt;&gt;()])
;
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
01 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

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<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - Overview</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Overview</h2>
</td>
</tr>
</table>
<hr>
<dl class="index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#topic1">First topic</a></dt>
<dt><a href="#topic2">Second topic</a></dt>
<dt><a href="#footnotes">Footnotes</a></dt>
</dl>
<h2><a name="introduction"></a>Introduction</h2>
<p>{{text}}</p>
<h2><a name="topic1"></a>First Topic</h2>
<p>{{text}}</p>
<h2><a name="topic2"></a>Second Topic</h2>
<p>{{text}}</p>
<h2><a name="footnotes"></a>Footnotes</h2>
<dl>
<dt><a name="footnote1" class="footnote">(1)</a> {{text}}</dt>
<dt><a name="footnote2" class="footnote">(2)</a> {{text}}</dt>
</dl>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
05 November, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a>
2002. All Rights Reserved.</i></p>
</body>
</html>

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<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN"
"http://www.w3.org/TR/REC-html40/strict.dtd">
<title>Boost.Python Pickle Support</title>
<div>
<img src="../../../../c++boost.gif"
alt="c++boost.gif (8819 bytes)"
align="center"
width="277" height="86">
<hr>
<h1>Boost.Python Pickle Support</h1>
Pickle is a Python module for object serialization, also known
as persistence, marshalling, or flattening.
<p>
It is often necessary to save and restore the contents of an object to
a file. One approach to this problem is to write a pair of functions
that read and write data from a file in a special format. A powerful
alternative approach is to use Python's pickle module. Exploiting
Python's ability for introspection, the pickle module recursively
converts nearly arbitrary Python objects into a stream of bytes that
can be written to a file.
<p>
The Boost Python Library supports the pickle module
through the interface as described in detail in the
<a href="http://www.python.org/doc/current/lib/module-pickle.html"
>Python Library Reference for pickle.</a> This interface
involves the special methods <tt>__getinitargs__</tt>,
<tt>__getstate__</tt> and <tt>__setstate__</tt> as described
in the following. Note that Boost.Python is also fully compatible
with Python's cPickle module.
<hr>
<h2>The Boost.Python Pickle Interface</h2>
At the user level, the Boost.Python pickle interface involves three special
methods:
<dl>
<dt>
<strong><tt>__getinitargs__</tt></strong>
<dd>
When an instance of a Boost.Python extension class is pickled, the
pickler tests if the instance has a <tt>__getinitargs__</tt> method.
This method must return a Python tuple (it is most convenient to use
a boost::python::tuple). When the instance is restored by the
unpickler, the contents of this tuple are used as the arguments for
the class constructor.
<p>
If <tt>__getinitargs__</tt> is not defined, <tt>pickle.load</tt>
will call the constructor (<tt>__init__</tt>) without arguments;
i.e., the object must be default-constructible.
<p>
<dt>
<strong><tt>__getstate__</tt></strong>
<dd>
When an instance of a Boost.Python extension class is pickled, the
pickler tests if the instance has a <tt>__getstate__</tt> method.
This method should return a Python object representing the state of
the instance.
<p>
<dt>
<strong><tt>__setstate__</tt></strong>
<dd>
When an instance of a Boost.Python extension class is restored by the
unpickler (<tt>pickle.load</tt>), it is first constructed using the
result of <tt>__getinitargs__</tt> as arguments (see above). Subsequently
the unpickler tests if the new instance has a <tt>__setstate__</tt>
method. If so, this method is called with the result of
<tt>__getstate__</tt> (a Python object) as the argument.
</dl>
The three special methods described above may be <tt>.def()</tt>'ed
individually by the user. However, Boost.Python provides an easy to use
high-level interface via the
<strong><tt>boost::python::pickle_suite</tt></strong> class that also
enforces consistency: <tt>__getstate__</tt> and <tt>__setstate__</tt>
must be defined as pairs. Use of this interface is demonstrated by the
following examples.
<hr>
<h2>Examples</h2>
There are three files in <a href="../../test/"
><tt>boost/libs/python/test</tt></a> that show how to
provide pickle support.
<hr>
<h3><a href="../../test/pickle1.cpp"><tt>pickle1.cpp</tt></a></h3>
The C++ class in this example can be fully restored by passing the
appropriate argument to the constructor. Therefore it is sufficient
to define the pickle interface method <tt>__getinitargs__</tt>.
This is done in the following way:
<ul>
<li>1. Definition of the C++ pickle function:
<pre>
struct world_pickle_suite : boost::python::pickle_suite
{
static
boost::python::tuple
getinitargs(world const&amp; w)
{
return boost::python::make_tuple(w.get_country());
}
};
</pre>
<li>2. Establishing the Python binding:
<pre>
class_&lt;world&gt;("world", args&lt;const std::string&amp;&gt;())
// ...
.def_pickle(world_pickle_suite())
// ...
</pre>
</ul>
<hr>
<h3><a href="../../test/pickle2.cpp"><tt>pickle2.cpp</tt></a></h3>
The C++ class in this example contains member data that cannot be
restored by any of the constructors. Therefore it is necessary to
provide the <tt>__getstate__</tt>/<tt>__setstate__</tt> pair of
pickle interface methods:
<ul>
<li>1. Definition of the C++ pickle functions:
<pre>
struct world_pickle_suite : boost::python::pickle_suite
{
static
boost::python::tuple
getinitargs(const world&amp; w)
{
// ...
}
static
boost::python::tuple
getstate(const world&amp; w)
{
// ...
}
static
void
setstate(world&amp; w, boost::python::tuple state)
{
// ...
}
};
</pre>
<li>2. Establishing the Python bindings for the entire suite:
<pre>
class_&lt;world&gt;("world", args&lt;const std::string&amp;&gt;())
// ...
.def_pickle(world_pickle_suite())
// ...
</pre>
</ul>
<p>
For simplicity, the <tt>__dict__</tt> is not included in the result
of <tt>__getstate__</tt>. This is not generally recommended, but a
valid approach if it is anticipated that the object's
<tt>__dict__</tt> will always be empty. Note that the safety guard
described below will catch the cases where this assumption is violated.
<hr>
<h3><a href="../../test/pickle3.cpp"><tt>pickle3.cpp</tt></a></h3>
This example is similar to <a
href="../../test/pickle2.cpp"><tt>pickle2.cpp</tt></a>. However, the
object's <tt>__dict__</tt> is included in the result of
<tt>__getstate__</tt>. This requires a little more code but is
unavoidable if the object's <tt>__dict__</tt> is not always empty.
<hr>
<h2>Pitfall and Safety Guard</h2>
The pickle protocol described above has an important pitfall that the
end user of a Boost.Python extension module might not be aware of:
<p>
<strong>
<tt>__getstate__</tt> is defined and the instance's <tt>__dict__</tt>
is not empty.
</strong>
<p>
The author of a Boost.Python extension class might provide a
<tt>__getstate__</tt> method without considering the possibilities
that:
<p>
<ul>
<li>
his class is used in Python as a base class. Most likely the
<tt>__dict__</tt> of instances of the derived class needs to be
pickled in order to restore the instances correctly.
<p>
<li>
the user adds items to the instance's <tt>__dict__</tt> directly.
Again, the <tt>__dict__</tt> of the instance then needs to be
pickled.
</ul>
<p>
To alert the user to this highly unobvious problem, a safety guard is
provided. If <tt>__getstate__</tt> is defined and the instance's
<tt>__dict__</tt> is not empty, Boost.Python tests if the class has
an attribute <tt>__getstate_manages_dict__</tt>. An exception is
raised if this attribute is not defined:
<pre>
RuntimeError: Incomplete pickle support (__getstate_manages_dict__ not set)
</pre>
To resolve this problem, it should first be established that the
<tt>__getstate__</tt> and <tt>__setstate__</tt> methods manage the
instances's <tt>__dict__</tt> correctly. Note that this can be done
either at the C++ or the Python level. Finally, the safety guard
should intentionally be overridden. E.g. in C++ (from
<a href="../../test/pickle3.cpp"><tt>pickle3.cpp</tt></a>):
<pre>
struct world_pickle_suite : boost::python::pickle_suite
{
// ...
static bool getstate_manages_dict() { return true; }
};
</pre>
Alternatively in Python:
<pre>
import your_bpl_module
class your_class(your_bpl_module.your_class):
__getstate_manages_dict__ = 1
def __getstate__(self):
# your code here
def __setstate__(self, state):
# your code here
</pre>
<hr>
<h2>Practical Advice</h2>
<ul>
<li>
In Boost.Python extension modules with many extension classes,
providing complete pickle support for all classes would be a
significant overhead. In general complete pickle support should
only be implemented for extension classes that will eventually
be pickled.
<p>
<li>
Avoid using <tt>__getstate__</tt> if the instance can also be
reconstructed by way of <tt>__getinitargs__</tt>. This automatically
avoids the pitfall described above.
<p>
<li>
If <tt>__getstate__</tt> is required, include the instance's
<tt>__dict__</tt> in the Python object that is returned.
</ul>
<hr>
&copy; Copyright Ralf W. Grosse-Kunstleve 20012-2002. Permission to copy,
use, modify, sell and distribute this document is granted provided this
copyright notice appears in all copies. This document is provided "as
is" without express or implied warranty, and with no claim as to its
suitability for any purpose.
<p>
Updated: Aug 2002.
</div>

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<title>Boost.Python - &lt;boost/python/pointee.hpp&gt;</title>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/pointee.hpp&gt;</h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a>
<dt><a href="#classes">Classes</a>
<dd>
<dl class="page-index">
<dt><a href="#pointee-spec">Class Template<code>pointee</code></a>
<dd>
<dl class="page-index">
<dt><a href="#pointee-spec-synopsis">Class Template
<code>pointee</code> synopsis</a>
</dl>
</dl>
<dt><a href="#examples">Example</a>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/pointee.hpp&gt;</code> introduces a
traits <a
href="../../../mpl/doc/index.html#metafunctions">metafunction</a>
template <code>pointee&lt;T&gt;</code> which can be used to extract the &quot;pointed-to&quot; type from the type of a pointer or smart pointer.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="pointee-spec"></a>Class Template <code>pointee&lt;class T&gt;</code></h3>
<p><code>pointee&lt;T&gt;</code> is used by the <code><a
href="class.html#class_-spec">class_</a>&lt;...&gt;</code>
template to deduce the type being held when a pointer or smart
pointer type is used as its <code>HeldType</code> argument.
<h4><a name="pointee-spec-synopsis"></a>Class Template
<code>pointee</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class T&gt; struct pointee
{
typedef T::element_type type;
};
// specialization for pointers
template &lt;T&gt; struct pointee&lt;T*&gt;
{
typedef T type;
};
}
</pre>
<h2><a name="examples"></a>Example</h2>
Given a 3rd-party smart pointer type
<code>smart_pointer&lt;T&gt;</code>, one might partially specialize
<code>pointee&lt;smart_pointer&ltT&gt; &gt;</code> so that it can be
used as the <code>HeldType</code> for a class wrapper:
<pre>
#include &lt;boost/python/pointee.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;third_party_lib.hpp&gt;
namespace boost { namespace python
{
template &lt;class T&gt; struct pointee&ltsmart_pointer&lt;T&gt; &gt;
{
typedef T type;
};
}}
BOOST_PYTHON_MODULE(pointee_demo)
{
class_&lt;third_party_class, smart_pointer&lt;third_party_class&gt; &gt;(&quot;third_party_class&quot;)
.def(...)
...
;
}
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
03 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>

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@@ -1,44 +0,0 @@
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - Progress Reports</title>
</head>
<body link="#0000ff" vlink="#800080">
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Progress Reports</h2>
</td>
</tr>
</table>
<hr>
Monthly progress reports are required as part of Boost Consulting's
contract with LLNL for Boost.Python development. These reports contain
a useful record of the project history, including the rationale for
design decisions and links to relevant discussions.
<dl class="page-index">
<dt><a href="feb2002.html">February 2002</a></dt>
<dt><a href="Mar2002.html">March 2002</a></dt>
<dt><a href="Apr2002.html">April 2002</a></dt>
<dt><a href="May2002.html">May 2002</a></dt>
<dt><a href="Jun2002.html">June 2002</a></dt>
</dl>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
18 July, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave Abrahams</a>
2002. All Rights Reserved.</i></p>
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<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;boost/python/ptr.hpp&gt;</title>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/ptr.hpp&gt;</h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a>
<dt><a href="#functions">Functions</a>
<dd>
<dl class="page-index">
<dt><a href="#ptr-spec">ptr</a>
</dl>
<dt><a href="#classes">Classes</a>
<dd>
<dl class="page-index">
<dt><a href="#pointer_wrapper-spec">Class template <code>pointer_wrapper</code></a>
<dd>
<dl class="page-index">
<dt><a href="#pointer_wrapper-spec-synopsis">Class template <code>pointer_wrapper</code> synopsis</a>
<dt><a href="#pointer_wrapper-spec-types">Class
<code>pointer_wrapper</code> types</a>
<dt><a href="#pointer_wrapper-spec-ctors">Class
<code>pointer_wrapper</code> constructors and destructor</a>
<dt><a href="#pointer_wrapper-spec-observers">Class
<code>pointer_wrapper</code> observer functions</a>
</dl>
</dl>
<dt><a href="#metafunctions">Metafunctions</a>
<dd>
<dl class="page-index">
<dt><a href="#is_pointer_wrapper-spec">Class template <code>is_pointer_wrapper</code></a>
<dd>
<dl class="page-index">
<dt><a href="#is_pointer_wrapper-spec-synopsis">Class template <code>is_pointer_wrapper</code> synopsis</a>
</dl>
<dt><a href="#unwrap_pointer-spec">Class template <code>unwrap_pointer</code></a>
<dd>
<dl class="page-index">
<dt><a href="#unwrap_pointer-spec-synopsis">Class template <code>unwrap_pointer</code> synopsis</a>
</dl>
</dl>
<dt><a href="#examples">Example(s)</a>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p><code>&lt;boost/python/ptr.hpp&gt;</code> defines the
<code>ptr()</code> function template, which allows users to
specify how to convert C++ pointer values to python in the context
of implementing overridable virtual functions, invoking Python
callable objects, or explicitly converting C++ objects to
Python. Normally, when passing pointers to Python callbacks, the
pointee is copied to ensure that the Python object
never holds a dangling reference. To specify that the new Python
object should merely contain a copy of a pointer <code>p</code>,
the user can pass <code><a href="#ptr-spec">ptr</a>(p)</code> instead of passing
<code>p</code> directly. This interface is meant to mirror the use
of <a href="../../../bind/ref.html"><code>boost::ref()</code></a>,
which can be similarly used to prevent copying of referents.
<p><code>ptr(p)</code> returns an instance of <code><a
href="#pointer_wrapper-spec">pointer_wrapper&lt;&gt;</a></code>, which
can be detected using the <code><a
href="#is_pointer_wrapper-spec">is_pointer_wrapper&lt;&gt;</a></code>
metafunction; <code><a
href="#unwrap_pointer-spec">unwrap_pointer&lt;&gt;</a></code> is a
metafunction which extracts the original pointer type from a
<code>pointer_wrapper&lt;&gt;</code>. These classes can be thought
of as implementation details.
<h2><a name="functions"></a>Functions</h2>
<pre>
<a name="ptr-spec">template &lt;class T&gt;</a>
pointer_wrapper&lt;T&gt; ptr(T x);
</pre>
<dl class="ptr-semantics">
<dt><b>Requires:</b> <code>T</code> is a pointer type.
<dt><b>Returns:</b> <code><a href="#pointer_wrapper-spec">pointer_wrapper</a>&lt;T&gt;(x)</code>
<dt><b>Throws:</b> nothing.
</dl>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="pointer_wrapper-spec"></a>Class template <code>pointer_wrapper</code></h3>
<p>A &quot;type envelope&quot; which is returned by <a
href="#ptr-spec">ptr()</a>, used to indicate reference semantics
for pointers passed to Python callbacks.
<h4><a name="pointer_wrapper-spec-synopsis"></a>Class
<code>pointer_wrapper</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template&lt;class Ptr&gt; class pointer_wrapper
{
public:
typedef Ptr type;
explicit pointer_wrapper(Ptr x);
operator Ptr() const;
Ptr get() const;
};
}}
</pre>
<h4><a name="pointer_wrapper-spec-types"></a>Class template <code>pointer_wrapper</code> types</h4>
<pre>
typedef Ptr type;
</pre>
The type of the pointer being wrapped.
<h4><a name="pointer_wrapper-spec-ctors"></a>Class template <code>pointer_wrapper</code> constructors and
destructor</h4>
<pre>
explicit pointer_wrapper(Ptr x);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>Ptr</code> is a pointer type.
<dt><b>Effects:</b> Stores <code>x</code> in a the <code>pointer_wrapper&lt;&gt;</code>.
<dt><b>Throws:</b> nothing.
</dl>
<h4><a name="pointer_wrapper-spec-observers"></a>Class template <code>pointer_wrapper</code> observer
functions</h4>
<pre>
operator Ptr() const;
Ptr get() const;
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> a copy of the stored pointer.
<dt><b>Rationale:</b> <code>pointer_wrapper</code> is intended
to be a stand-in for the actual pointer type, but sometimes it's
better to have an explicit way to retrieve the pointer.
</dl>
<h2><a name="metafunctions"></a>Metafunctions</h2>
<h3><a name="is_pointer_wrapper-spec"></a>Class template <code>is_pointer_wrapper</code></h3>
<p>A unary metafunction whose <code>value</code> is true iff its
argument is a <code>pointer_wrapper&lt;&gt;</code>.
<h4><a name="is_pointer_wrapper-spec-synopsis"></a>Class template <code>is_pointer_wrapper</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template&lt;class T&gt; class is_pointer_wrapper
{
static <i>unspecified</i> value = ...;
};
}}
</pre>
<dl class="metafunction-semantics">
<dt><b>Returns:</b> <code>true</code> iff <code>T</code> is a
specialization of
<code>pointer_wrapper&lt;&gt;</code>.
<dt><code>value</code> is an integral constant convertible to bool of
unspecified type
</dl>
<h3><a name="unwrap_pointer-spec"></a>Class template <code>unwrap_pointer</code></h3>
A unary metafunction which extracts the wrapped pointer type from a
specialization of <code>pointer_wrapper&lt;&gt;</code>.
<h4><a name="unwrap_pointer-spec-synopsis"></a>Class template <code>unwrap_pointer</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template&lt;class T&gt; class unwrap_pointer
{
typedef <i>unspecified</i> type;
};
}}
</pre>
<dl class="metafunction-semantics">
<dt><b>Returns:</b> <code>T::type</code> if <code>T</code> is a
specialization of
<code>pointer_wrapper&lt;&gt;</code>, <code>T</code> otherwise
</dl>
<h2><a name="examples"></a>Example(s)</h2>
This example illustrates the use of <code>ptr()</code> to prevent an
object from being copied:
<pre>
#include &lt;boost/python/call.hpp&gt;
#include &lt;boost/python/ptr.hpp&gt;
class expensive_to_copy
{
...
};
void pass_as_arg(expensive_to_copy* x, PyObject* f)
{
// call the Python function f, passing a Python object built around
// which refers to *x by-pointer.
//
// *** Note: ensuring that *x outlives the argument to f() is ***
// *** up to the user! Failure to do so could result in a crash! ***
boost::python::call&lt;void&gt;(f, ptr(x));
}
...
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 May, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
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<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>This is a convenience header which #includes all of the public
interface headers that are part of the Boost.Python library</p>
<pre>
# include &lt;args.hpp&gt;
# include &lt;args_fwd.hpp&gt;
# include &lt;back_reference.hpp&gt;
# include &lt;bases.hpp&gt;
# include &lt;borrowed.hpp&gt;
# include &lt;call.hpp&gt;
# include &lt;call_method.hpp&gt;
# include &lt;class.hpp&gt;
# include &lt;copy_const_reference.hpp&gt;
# include &lt;copy_non_const_reference.hpp&gt;
# include &lt;data_members.hpp&gt;
# include &lt;def.hpp&gt;
# include &lt;default_call_policies.hpp&gt;
# include &lt;dict.hpp&gt;
# include &lt;enum.hpp&gt;
# include &lt;errors.hpp&gt;
# include &lt;exception_translator.hpp&gt;
# include &lt;extract.hpp&gt;
# include &lt;handle.hpp&gt;
# include &lt;has_back_reference.hpp&gt;
# include &lt;implicit.hpp&gt;
# include &lt;init.hpp&gt;
# include &lt;instance_holder.hpp&gt;
# include &lt;iterator.hpp&gt;
# include &lt;list.hpp&gt;
# include &lt;long.hpp&gt;
# include &lt;lvalue_from_pytype.hpp&gt;
# include &lt;make_function.hpp&gt;
# include &lt;manage_new_object.hpp&gt;
# include &lt;module.hpp&gt;
# include &lt;numeric.hpp&gt;
# include &lt;object.hpp&gt;
# include &lt;object_protocol.hpp&gt;
# include &lt;object_protocol_core.hpp&gt;
# include &lt;operators.hpp&gt;
# include &lt;other.hpp&gt;
# include &lt;overloads.hpp&gt;
# include &lt;pointee.hpp&gt;
# include &lt;ptr.hpp&gt;
# include &lt;reference_existing_object.hpp&gt;
# include &lt;return_internal_reference.hpp&gt;
# include &lt;return_value_policy.hpp&gt;
# include &lt;scope.hpp&gt;
# include &lt;self.hpp&gt;
# include &lt;slice_nil.hpp&gt;
# include &lt;str.hpp&gt;
# include &lt;to_python_converter.hpp&gt;
# include &lt;to_python_indirect.hpp&gt;
# include &lt;to_python_value.hpp&gt;
# include &lt;tuple.hpp&gt;
# include &lt;type_id.hpp&gt;
# include &lt;with_custodian_and_ward.hpp&gt;
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
08 October, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
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</body>
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<head>
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<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - Rationale</title>
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<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Rationale</h2>
</td>
</tr>
</table>
<hr>
<dl class="index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#topic1">First topic</a></dt>
<dt><a href="#topic2">Second topic</a></dt>
<dt><a href="#footnotes">Footnotes</a></dt>
</dl>
<h2><a name="introduction"></a>Introduction</h2>
<p>{{text}}</p>
<h2><a name="topic1"></a>First Topic</h2>
<p>{{text}}</p>
<h2><a name="topic2"></a>Second Topic</h2>
<p>{{text}}</p>
<h2><a name="footnotes"></a>Footnotes</h2>
<dl>
<dt><a name="footnote1" class="footnote">(1)</a> {{text}}</dt>
<dt><a name="footnote2" class="footnote">(2)</a> {{text}}</dt>
</dl>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
05 November, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
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<title>Boost.Python - Reference</title>
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alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
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<h1 class="c1">Boost.Python</h1>
<h2 class="c2">Reference</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="Reference">
<dt><a href="#concepts">Concepts</a></dt>
<dt><a href="#high_level">High Level Components</a></dt>
<dt><a href="#object_wrappers">Object Wrappers</a></dt>
<dt><a href="#invocation">Function Invocation and Creation</a></dt>
<dd>
<dl class="index">
<dt><a href="#models_of_call_policies">Models of
CallPolicies</a></dt>
<dt><a href="#models_of_result_converter">Models of
ResultConverter</a></dt>
<dt><a href="#result_converter_generators">Models of
ResultConverterGenerator</a></dt>
</dl>
</dd>
<dt><a href="#type_conversion">To/From Python Type Conversion</a></dt>
<dt><a href="#utility">Utility and Infrastructure</a></dt>
<dt><a href="#topics">Topics</a></dt>
</dl>
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<dt><a href=
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<dt><a href=
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<dd>
<dl class="index">
<dt><a href="class.html#classes">Classes</a></dt>
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<dt><a href="class.html#bases-spec">bases</a></dt>
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<dl class="page-index">
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<dd>
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<dt><a href="enum.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href="enum.html#enum_-spec">enum_</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="errors.html">errors.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="errors.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href=
"errors.html#error_already_set-spec">error_already_set</a></dt>
</dl>
</dd>
<dt><a href="errors.html#functions">Functions</a></dt>
<dd>
<dl class="index">
<dt><a href=
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<dt><a href=
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<dt><a href=
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</dl>
</dd>
</dl>
</dd>
<dt><a href=
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<dd>
<dl class="index">
<dt><a href=
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<dd>
<dl class="index">
<dt><a href=
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</dl>
</dd>
</dl>
</dd>
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<dd>
<dl class="index">
<dt><a href="init.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href="init.html#init-spec">init</a></dt>
<dt><a href="init.html#optional-spec">optional</a></dt>
</dl>
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<dd>
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with_custodian_and_ward</a></dt>
<dt><a href=
"with_custodian_and_ward.html#with_custodian_and_ward_postcall-spec">
with_custodian_and_ward_postcall</a></dt>
</dl>
</dd>
</dl>
</dd>
</dl>
<a name="models_of_result_converter"></a>
<h3>Models of ResultConverter</h3>
<dl class="index">
<dt><a href=
"to_python_indirect.html">to_python_indirect.hpp</a></dt>
<dd>
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<dt><a href=
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</dl>
</dd>
</dl>
</dd>
<dt><a href="to_python_value.html">to_python_value.hpp</a></dt>
<dd>
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<dd>
<dl class="index">
<dt><a href=
"to_python_value.html#to_python_value-spec">to_python_value</a></dt>
</dl>
</dd>
</dl>
</dd>
</dl>
<a name="result_converter_generators"></a>
<h3>Models of ResultConverterGenerator</h3>
<dl class="index">
<dt><a href=
"copy_const_reference.html">copy_const_reference.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href=
"copy_const_reference.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href=
"copy_const_reference.html#copy_const_reference-spec">copy_const_reference</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href=
"copy_non_const_reference.html">copy_non_const_reference.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href=
"copy_non_const_reference.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href=
"copy_non_const_reference.html#copy_non_const_reference-spec">
copy_non_const_reference</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="manage_new_object.html">manage_new_object.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="manage_new_object.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href=
"manage_new_object.html#manage_new_object-spec">manage_new_object</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href=
"reference_existing_object.html">reference_existing_object.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href=
"reference_existing_object.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href=
"reference_existing_object.html#reference_existing_object-spec">
reference_existing_object</a></dt>
</dl>
</dd>
</dl>
</dd>
</dl>
</dd>
</dl>
<h2><a name="type_conversion">To/From Python Type Conversion</a></h2>
<dl class="index">
<dt><a href="extract.html">extract.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="extract.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href="extract.html#extract-spec">extract</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="implicit.html">implicit.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="implicit.html#functions">Functions</a></dt>
<dd>
<dl class="index">
<dt><a href=
"implicit.html#implicitly_convertible-spec">implicitly_convertible</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="lvalue_from_pytype.html">lvalue_from_pytype.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="lvalue_from_pytype.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href=
"lvalue_from_pytype.html#lvalue_from_pytype-spec">lvalue_from_pytype</a></dt>
<dt><a href=
"lvalue_from_pytype.html#extract_identity-spec">extract_identity</a></dt>
<dt><a href=
"lvalue_from_pytype.html#extract_member-spec">extract_member</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="to_python_converter.html">to_python_converter.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="to_python_converter.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href=
"to_python_converter.html#to_python_converter-spec">to_python_converter</a></dt>
</dl>
</dd>
</dl>
</dd>
</dl>
<h2><a name="utility">Utility and Infrastructure</a></h2>
<dl>
<dt><a href="has_back_reference.html">has_back_reference.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="has_back_reference.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href=
"has_back_reference.html#has_back_reference-spec">has_back_reference</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="instance_holder.html">instance_holder.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="instance_holder.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href=
"instance_holder.html#instance_holder-spec">instance_holder</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="pointee.html">pointee.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="pointee.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt>class template <a href=
"pointee.html#pointee">pointee</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="python.html">&lt;boost/python.hpp&gt;</a></dt>
<dt><a href="handle.html">handle.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="handle.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href="handle.html#handle-spec">handle</a></dt>
</dl>
</dd>
<dt><a href="handle.html#functions">Functions</a></dt>
<dd>
<dl class="index">
<dt><a href="handle.html#borrowed-spec">borrowed</a></dt>
<dt><a href="handle.html#allow_null-spec">allow_null</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="type_id.html">type_id.hpp</a></dt>
<dd>
<dl class="index">
<dt><a href="type_id.html#functions">Functions</a></dt>
<dd>
<dl class="index">
<dt><a href="type_id.html#type_id-spec">type_id</a></dt>
</dl>
</dd>
<dt><a href="type_id.html#classes">Classes</a></dt>
<dd>
<dl class="index">
<dt><a href="type_id.html#type_info-spec">type_info</a></dt>
</dl>
</dd>
</dl>
</dd>
</dl>
<h2><a name="topics">Topics</a></h2>
<dl>
<dt><a href="callbacks.html">Calling Python Functions and
Methods</a></dt>
<dt><a href="pickle.html">Pickle Support</a></dt>
</dl>
<hr>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
3 June, 2002 <!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
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<title>Boost.Python -
&lt;boost/python/reference_existing_object.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
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<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/reference_existing_object.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#reference_existing_object-spec">Class
<code>reference_existing_object</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#reference_existing_object-spec-synopsis">Class
<code>reference_existing_object</code> synopsis</a></dt>
<dt><a href=
"#reference_existing_object-spec-metafunctions">Class
<code>reference_existing_object</code> metafunctions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="reference_existing_object-spec"></a>Class
<code>reference_existing_object</code></h3>
<p><code>reference_existing_object</code> is a model of <a href=
"ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a>
which can be used to wrap C++ functions which return a reference or
pointer to a C++ object. When the wrapped function is called, the value
referenced by its return value is not copied. A new Python object is
created which contains a pointer to the referent, and no attempt is made
to ensure that the lifetime of the referent is at least as long as that
of the corresponding Python object. Thus, it can be <font color=
"#ff0000"><b>highly dangerous</b></font> to use
<code>reference_existing_object</code> without additional lifetime
management from such models of <a href=
"CallPolicies.html">CallPolicies</a> as <a href=
"with_custodian_and_ward.html#with_custodian_and_ward-spec">with_custodian_and_ward</a>.
This class is used in the implementation of <a href=
"return_internal_reference.html#return_internal_reference-spec">return_internal_reference</a>.</p>
<h4><a name="reference_existing_object-spec-synopsis"></a>Class
<code>reference_existing_object</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
struct reference_existing_object
{
template &lt;class T&gt; struct apply;
};
}}
</pre>
<h4><a name="reference_existing_object-spec-metafunctions"></a>Class
<code>reference_existing_object</code> metafunctions</h4>
<pre>
template &lt;class T&gt; struct apply
</pre>
<dl class="metafunction-semantics">
<dt><b>Requires:</b> <code>T</code> is <code>U&amp;</code> or
<code>U*</code>for some <code>U</code>.</dt>
<dt><b>Returns:</b> <code>typedef <a href=
"to_python_indirect.html#to_python_indirect-spec">to_python_indirect</a>&lt;T,V&gt;
type</code>, where <code>V</code> is a <a href=
"to_python_indirect.html#HolderObjectGenerator">HolderObjectGenerator</a>
which constructs an instance holder containing an <i>unowned</i>
<code>U*</code> pointing to the referent of the wrapped function's
return value.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<p>In C++:</p>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/reference_existing_object.hpp&gt;
#include &lt;boost/python/return_value_policy.hpp&gt;
#include &lt;utility&gt;
// classes to wrap
struct Singleton
{
Singleton() : x(0) {}
int exchange(int n) // set x and return the old value
{
std::swap(n, x);
return n;
}
int x;
};
Singleton&amp; get_it()
{
static Singleton just_one;
return just_one;
}
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(singleton)
{
def("get_it", get_it, reference_existing_object());
class_&lt;Singleton&gt;("Singleton")
.def("exchange", &amp;Singleton::exchange)
;
}
</pre>
In Python:
<pre>
&gt;&gt;&gt; import singleton
&gt;&gt;&gt; s1 = singleton.get_it()
&gt;&gt;&gt; s2 = singleton.get_it()
&gt;&gt;&gt; id(s1) == id(s2) # s1 and s2 are not the same object
0
&gt;&gt;&gt; s1.exchange(42) # but they reference the same C++ Singleton
0
&gt;&gt;&gt; s2.exchange(99)
42
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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<title>Boost.Python -
&lt;boost/python/return_internal_reference.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/return_internal_reference.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#return_internal_reference-spec">Class Template
<code>return_internal_reference</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#return_internal_reference-spec-synopsis">Class
Template <code>return_internal_reference</code>
synopsis</a></dt>
<dt><a href="#return_internal_reference-spec-statics">Class
<code>return_internal_reference</code> static
functions</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<code>return_internal_reference</code> instantiations are models of <a
href="CallPolicies.html">CallPolicies</a> which allow pointers and
references to objects held internally by a free or member function
argument or from the target of a member function to be returned safely
without making a copy of the referent. The default for its first template
argument handles the common case where the containing object is the
target (<code>*this</code>) of a wrapped member function.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="return_internal_reference-spec"></a>Class template
<code>return_internal_reference</code></h3>
<table border="1" summary=
"return_internal_reference template parameters">
<caption>
<b><code>return_internal_reference</code> template parameters</b>
</caption>
<tr>
<th>Parameter</th>
<th>Requirements</th>
<th>Description</th>
<th>Default</th>
</tr>
<tr>
<td><code>owner_arg</code></td>
<td>A positive compile-time constant of type
<code>std::size_t</code>.</td>
<td>The index of the parameter which contains the object to which the
reference or pointer is being returned. If used to wrap a member
function, parameter 1 is the target object (<code>*this</code>). Note
that if the target Python object type doesn't support weak
references, a Python <code>TypeError</code> exception will be raised
when the function being wrapped is called.</td>
<td>1</td>
</tr>
<tr>
<td><code>Base</code></td>
<td>A model of <a href="CallPolicies.html">CallPolicies</a></td>
<td>Used for policy composition. Any <code>result_converter</code> it
supplies will be overridden by
<code>return_internal_reference</code>, but its <code>precall</code>
and <code>postcall</code> policies are composed as described here <a
href="CallPolicies.html#composition">CallPolicies</a>.</td>
<td><code><a href=
"default_call_policies.html#default_call_policies-spec">default_call_policies</a></code></td>
</tr>
</table>
<h4><a name="return_internal_reference-spec-synopsis"></a>Class template
<code>return_internal_reference</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;std::size_t owner_arg = 1, class Base = default_call_policies&gt;
struct return_internal_reference : Base
{
static PyObject* postcall(PyObject*, PyObject* result);
typedef <a href=
"reference_existing_object.html#reference_existing_object-spec">reference_existing_object</a> result_converter;
};
}}
</pre>
<h4><a name="default_call_policies-spec-statics"></a>Class
<code>default_call_policies</code> static functions</h4>
<pre>
PyObject* postcall(PyObject* args, PyObject* result);
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code><a href=
"http://www.python.org/doc/2.2/api/tupleObjects.html#l2h-476">PyTuple_Check</a>(args)
!= 0</code></dt>
<dt><b>Returns:</b> <code><a href=
"with_custodian_and_ward.html#with_custodian_and_ward_postcall-spec-statics">
with_custodian_and_ward_postcall::postcall(args,
result)</a></code></dt>
</dl>
<h2><a name="examples"></a>Example</h2>
<h3>C++ module definition</h3>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/return_internal_reference.hpp&gt;
class Bar
{
Bar(int x) : x(x) {}
int get_x() const { return x; }
void set_x(int x) { this-&gt;x = x; }
private:
int x;
}
class Foo
{
public:
Foo(int x) : b(x) {}
// Returns an internal reference
Bar const&amp; get_bar() const { return b; }
private:
Bar b;
};
using namespace boost::python;
BOOST_PYTHON_MODULE(internal_refs)
{
class_&lt;Bar&gt;("Bar")
.def("get_x", &amp;Bar::get_x)
.def("set_x", &amp;Bar::set_x)
;
class_&lt;Foo&gt;("Foo", init&lt;int&gt;())
.def("get_bar", &amp;Foo::get_bar
, return_internal_reference&lt;&gt;())
;
}
</pre>
<h3>Python code</h3>
<pre>
&gt;&gt;&gt; from internal_refs import *
&gt;&gt;&gt; f = Foo(3)
&gt;&gt;&gt; b1 = f.get_bar()
&gt;&gt;&gt; b2 = f.get_bar()
&gt;&gt;&gt; b1.get_x()
3
&gt;&gt;&gt; b2.get_x()
3
&gt;&gt;&gt; b1.set_x(42)
&gt;&gt;&gt; b2.get_x()
42
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
15 February, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
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</html>

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<title>Boost.Python -
&lt;boost/python/return_value_policy.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/return_value_policy.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#return_value_policy-spec">Class Template
<code>return_value_policy</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#return_value_policy-spec-synopsis">Class Template
<code>return_value_policy</code> synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<code>return_value_policy</code> instantiations are simply models of <a
href="CallPolicies.html">CallPolicies</a> which are composed of a <a
href=
"ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a>
and optional <code>Base</code> <a href=
"CallPolicies.html">CallPolicies</a>.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="return_value_policy-spec"></a>Class template
<code>return_value_policy</code></h3>
<table border="1" summary="return_value_policy template parameters">
<caption>
<b><code>return_value_policy</code> template parameters</b>
</caption>
<tr>
<th>Parameter</th>
<th>Requirements</th>
<th>Default</th>
</tr>
<tr>
<td><a href=
"ResultConverter.html#ResultConverterGenerator-concept">ResultConverterGenerator</a></td>
<td>A model of <a href=
"ResultConverterGenerator.html">ResultConverterGenerator</a>.</td>
</tr>
<tr>
<td><code>Base</code></td>
<td>A model of <a href="CallPolicies.html">CallPolicies</a></td>
<td><code><a href=
"default_call_policies.html#default_call_policies-spec">default_call_policies</a></code></td>
</tr>
</table>
<h4><a name="return_value_policy-spec-synopsis"></a>Class template
<code>return_value_policy</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class ResultConverterGenerator, class Base = default_call_policies&gt;
struct return_value_policy : Base
{
typedef ResultConverterGenerator result_converter;
};
}}
</pre>
<h2><a name="examples"></a>Example</h2>
<h3>C++ Module Definition</h3>
<pre>
#include &lt;boost/python/module.hpp&gt;
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/copy_const_reference.hpp&gt;
#include &lt;boost/python/return_value_policy.hpp&gt;
// classes to wrap
struct Bar { int x; }
struct Foo {
Foo(int x) : { b.x = x; }
Bar const&amp; get_bar() const { return b; }
private:
Bar b;
};
// Wrapper code
using namespace boost::python;
BOOST_PYTHON_MODULE(my_module)
{
class_&lt;Bar&gt;("Bar");
class_&lt;Foo&gt;("Foo", init&lt;int&gt;())
.def("get_bar", &amp;Foo::get_bar
, return_value_policy&lt;copy_const_reference&gt;())
;
}
</pre>
<h3>Python Code</h3>
<pre>
&gt;&gt;&gt; from my_module import *
&gt;&gt;&gt; f = Foo(3) # create a Foo object
&gt;&gt;&gt; b = f.get_bar() # make a copy of the internal Bar object
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
15 February, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

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<head>
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<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;boost/python/scope.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/scope.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#scope-spec">Class <code>scope</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#scope-spec-synopsis">Class <code>scope</code>
synopsis</a></dt>
<dt><a href="#scope-spec-ctors">Class <code>scope</code>
constructors and destructor</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>Defines facilities for querying and controlling the Python scope
(namespace) which will contain new wrapped classes and functions.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="scope-spec"></a>Class <code>scope</code></h3>
<p>The <code>scope</code> class has an associated global Python
object which controls the Python namespace in which new extension
classes and wrapped functions will be defined as
attributes. Default-constructing a new <code>scope</code> object
binds it to the associated global Python object. Constructing a
<code>scope</code> object with an argument changes the associated
global Python object to the one held by the argument, until the
lifetime of the <code>scope</code> object ends, at which time the
associated global Python object reverts to what it was before the
<code>scope</code> object was constructed.</p>
<h4><a name="scope-spec-synopsis"></a>Class <code>scope</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
class scope : public <a href=
"object.html#object-spec">object</a>, private <a href=
"../../../utility/utility.htm#Class noncopyable">noncopyable</a>
{
public:
scope(object const&amp;);
scope();
~scope()
};
}}
</pre>
<h4><a name="scope-spec-ctors"></a>Class <code>scope</code> constructors
and destructor</h4>
<pre>
scope(object const&amp; x);
</pre>
Stores a reference to the current associated scope object, and sets the
associated scope object to the one referred to by <code>x.ptr()</code>.
The <code>object</code> base class is initialized with <code>x</code>.
<pre>
scope();
</pre>
Stores a reference to the current associated scope object. The
<code>object</code> base class is initialized with the current associated
scope object. Outside any module initialization function, the current
associated Python object is <code>None</code>.
<pre>
~scope()
</pre>
Sets the current associated Python object to the stored object.
<h2><a name="examples"></a>Example</h2>
The following example shows how scope setting can be used to define
nested classes.
<p>C++ Module definition:</p>
<pre>
#include &lt;boost/python/class.hpp&gt;
#include &lt;boost/python/scope.hpp&gt;
using namespace boost::python;
struct X
{
void f();
struct Y { int g() { return 42; } };
};
BOOST_PYTHON_MODULE(nested)
{
// add some constants to the current (module) scope
scope().attr("yes") = 1;
scope().attr("no") = 0;
// Change the current scope
scope outer
= class_&lt;X&gt;("X")
.def("f", &amp;X::f)
;
// Define a class Y in the current scope, X
class_&lt;Y&gt;("Y")
.def("g", &amp;Y::g)
;
}
</pre>
Interactive Python:
<pre>
&gt;&gt;&gt; import nested
&gt;&gt;&gt; nested.yes
1
&gt;&gt;&gt; y = nested.X.Y()
&gt;&gt;&gt; y.g()
42
</pre>
<p>Revised 03 October, 2002</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

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<html>
<head>
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;boost/python/str.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/str.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#str-spec">Class <code>str</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#str-spec-synopsis">Class <code>str</code>
synopsis</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example(s)</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<p>Exposes a <a href=
"ObjectWrapper.html#TypeWrapper-concept">TypeWrapper</a> for the Python
<a href=
"http://www.python.org/dev/doc/devel/lib/string-methods.html">str</a>
type.</p>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="str-spec"></a>Class <code>str</code></h3>
<p>Exposes the <a href=
"http://www.python.org/dev/doc/devel/lib/string-methods.html">string
methods</a> of Python's built-in <code>str</code> type. The
semantics of the constructors and member functions defined below
can be fully understood by reading the <a href=
"ObjectWrapper.html#TypeWrapper-concept">TypeWrapper</a> concept
definition. Since <code>str</code> is publicly derived from
<code><a href="object.html#object-spec">object</a></code>, the
public object interface applies to <code>str</code> instances as
well.</p>
<h4><a name="str-spec-synopsis"></a>Class <code>str</code>
synopsis</h4>
<pre>
namespace boost { namespace python
{
class str : public object
{
public:
str(); // new str
str(const char* s); // new str
template &lt;class T&gt;
explicit str(T const&amp; other);
str capitalize() const;
template &lt;class T&gt;
str center(T const&amp; width) const;
template&lt;class T&gt;
long count(T const&amp; sub) const;
template&lt;class T1, class T2&gt;
long count(T1 const&amp; sub,T2 const&amp; start) const;
template&lt;class T1, class T2, class T3&gt;
long count(T1 const&amp; sub,T2 const&amp; start, T3 const&amp; end) const;
object decode() const;
template&lt;class T&gt;
object decode(T const&amp; encoding) const;
template&lt;class T1, class T2&gt;
object decode(T1 const&amp; encoding, T2 const&amp; errors) const;
object encode() const;
template &lt;class T&gt;
object encode(T const&amp; encoding) const;
template &lt;class T1, class T2&gt;
object encode(T1 const&amp; encoding, T2 const&amp; errors) const;
template &lt;class T&gt;
bool endswith(T const&amp; suffix) const;
template &lt;class T1, class T2&gt;
bool endswith(T1 const&amp; suffix, T2 const&amp; start) const;
template &lt;class T1, class T2, class T3&gt;
bool endswith(T1 const&amp; suffix, T2 const&amp; start, T3 const&amp; end) const;
str expandtabs() const;
template &lt;class T&gt;
str expandtabs(T const&amp; tabsize) const;
template &lt;class T&gt;
long find(T const&amp; sub) const;
template &lt;class T1, class T2&gt;
long find(T1 const&amp; sub, T2 const&amp; start) const;
template &lt;class T1, class T2, class T3&gt;
long find(T1 const&amp; sub, T2 const&amp; start, T3 const&amp; end) const;
template &lt;class T&gt;
long index(T const&amp; sub) const;
template &lt;class T1, class T2&gt;
long index(T1 const&amp; sub, T2 const&amp; start) const;
template &lt;class T1, class T2, class T3&gt;
long index(T1 const&amp; sub, T2 const&amp; start, T3 const&amp; end) const;
bool isalnum() const;
bool isalpha() const;
bool isdigit() const;
bool islower() const;
bool isspace() const;
bool istitle() const;
bool isupper() const;
template &lt;class T&gt;
str join(T const&amp; sequence) const;
template &lt;class T&gt;
str ljust(T const&amp; width) const;
str lower() const;
str lstrip() const;
template &lt;class T1, class T2&gt;
str replace(T1 const&amp; old, T2 const&amp; new_) const;
template &lt;class T1, class T2, class T3&gt;
str replace(T1 const&amp; old, T2 const&amp; new_, T3 const&amp; maxsplit) const;
template &lt;class T&gt;
long rfind(T const&amp; sub) const;
template &lt;class T1, class T2&gt;
long rfind(T1 const&amp; sub, T2 const&amp; start) const;
template &lt;class T1, class T2, class T3&gt;
long rfind(T1 const&amp; sub, T2 const&amp; start, T3 const&amp; end) const;
template &lt;class T&gt;
long rindex(T const&amp; sub) const;
template &lt;class T1, class T2&gt;
long rindex(T1 const&amp; sub, T2 const&amp; start) const;
template &lt;class T1, class T2, class T3&gt;
long rindex(T1 const&amp; sub, T2 const&amp; start, T3 const&amp; end) const;
template &lt;class T&gt;
str rjust(T const&amp; width) const;
str rstrip() const;
list split() const;
template &lt;class T&gt;
list split(T const&amp; sep) const;
template &lt;class T1, class T2&gt;
list split(T1 const&amp; sep, T2 const&amp; maxsplit) const;
list splitlines() const;
template &lt;class T&gt;
list splitlines(T const&amp; keepends) const;
template &lt;class T&gt;
bool startswith(T const&amp; prefix) const;
template &lt;class T1, class T2&gt;
bool startswidth(T1 const&amp; prefix, T2 const&amp; start) const;
template &lt;class T1, class T2, class T3&gt;
bool startswidth(T1 const&amp; prefix, T2 const&amp; start, T3 const&amp; end) const;
str strip() const;
str swapcase() const;
str title() const;
template &lt;class T&gt;
str translate(T const&amp; table) const;
template &lt;class T1, class T2&gt;
str translate(T1 const&amp; table, T2 const&amp; deletechars) const;
str upper() const;
};
}}
</pre>
<h2><a name="examples"></a>Example</h2>
<pre>
using namespace boost::python;
str remove_angle_brackets(str x)
{
return x.strip('&lt;').strip('&gt;');
}
</pre>
<p>Revised 3 October, 2002</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

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<html>
<head>
<meta name="generator" content=
"HTML Tidy for Windows (vers 1st August 2002), see www.w3.org">
<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python -
&lt;boost/python/to_python_converter.hpp&gt;</title>
</head>
<body>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277"
alt="C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
</td>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/to_python_converter.hpp&gt;</h2>
</td>
</tr>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a></dt>
<dt><a href="#classes">Classes</a></dt>
<dd>
<dl class="page-index">
<dt><a href="#to_python_converter-spec">Class Template
<code>to_python_converter</code></a></dt>
<dd>
<dl class="page-index">
<dt><a href="#to_python_converter-spec-synopsis">Class Template
<code>to_python_converter</code> synopsis</a></dt>
<dt><a href="#to_python_converter-spec-ctors">Class Template
<code>to_python_converter</code> constructor</a></dt>
</dl>
</dd>
</dl>
</dd>
<dt><a href="#examples">Example</a></dt>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<code>to_python_converter</code> registers a conversion from objects of a
given C++ type into a Python object.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="to_python_converter-spec"></a>Class template
<code>to_python_converter</code></h3>
<code>to_python_converter</code> adds a wrapper around a static member
function of its second template parameter, handling low-level details
such as insertion into the converter registry.
<table border="1" summary="to_python_converter template parameters">
<caption>
<b><code>to_python_converter</code> template parameters</b><br>
In the table below, <b><code>x</code></b> denotes an object of type
<code>T</code>
</caption>
<tr>
<th>Parameter</th>
<th>Requirements</th>
<th>Description</th>
</tr>
<tr>
<td><code>T</code></td>
<td>
</td>
<td>The C++ type of the source object in the conversion</td>
</tr>
<tr>
<td><code>Conversion</code></td>
<td>
<code>PyObject*&nbsp;p&nbsp;=&nbsp;Conversion::convert(x)</code>,<br>
if <code>p&nbsp;==&nbsp;0</code>, <code><a href=
"http://www.python.org/doc/2.2/api/exceptionHandling.html#l2h-71">PyErr_Occurred</a>()&nbsp;!=&nbsp;0</code>.</td>
<td>A class type whose static member function <code>convert</code>
does the real work of the conversion.</td>
</tr>
</table>
<h4><a name="to_python_converter-spec-synopsis"></a>Class template
<code>to_python_converter</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class T, class Conversion&gt;
struct to_python_converter
{
to_python_converter();
};
}}
</pre>
<h4><a name="to_python_converter-spec-ctors"></a>Class template
<code>to_python_converter</code> constructor</h4>
<pre>
to_python_converter();
</pre>
<dl class="function-semantics">
<dt><b>Effects:</b> Registers a to_python converter which uses
<code>Conversion::convert()</code> to do its work.</dt>
</dl>
<h2><a name="examples"></a>Example</h2>
This example presumes that someone has implemented the standard <a href=
"http://www.python.org/doc/2.2/ext/dnt-basics.html">noddy example
module</a> from the Python documentation, and placed the corresponding
declarations in <code>"noddy.h"</code>. Because
<code>noddy_NoddyObject</code> is the ultimate trivial extension type,
the example is a bit contrived: it wraps a function for which all
information is contained in the <i>type</i> of its return value.
<h3>C++ module definition</h3>
<pre>
#include &lt;boost/python/reference.hpp&gt;
#include &lt;boost/python/module.hpp&gt;
#include "noddy.h"
struct tag {};
tag make_tag() { return tag(); }
using namespace boost::python;
struct tag_to_noddy
{
static PyObject* convert(tag const&amp; x)
{
return PyObject_New(noddy_NoddyObject, &amp;noddy_NoddyType);
}
};
BOOST_PYTHON_MODULE(to_python_converter)
{
def("make_tag", make_tag);
to_python_converter&lt;tag, tag_to_noddy&gt;();
}
</pre>
<h3>Python code</h3>
<pre>
&gt;&gt;&gt; import to_python_converter
&gt;&gt;&gt; def always_none():
... return None
...
&gt;&gt;&gt; def choose_function(x):
... if (x % 2 != 0):
... return to_python_converter.make_tag
... else:
... return always_none
...
&gt;&gt;&gt; a = [ choose_function(x) for x in range(5) ]
&gt;&gt;&gt; b = [ f() for f in a ]
&gt;&gt;&gt; type(b[0])
&lt;type 'NoneType'&gt;
&gt;&gt;&gt; type(b[1])
&lt;type 'Noddy'&gt;
&gt;&gt;&gt; type(b[2])
&lt;type 'NoneType'&gt;
&gt;&gt;&gt; type(b[3])
&lt;type 'Noddy'&gt;
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
29 September, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
</p>
<p><i>&copy; Copyright <a href=
"../../../../people/dave_abrahams.htm">Dave Abrahams</a> 2002. All Rights
Reserved.</i></p>
</body>
</html>

View File

@@ -1,194 +0,0 @@
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<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1">
<link rel="stylesheet" type="text/css" href="../boost.css">
<title>Boost.Python - &lt;boost/python/to_python_indirect.hpp&gt;</title>
<table border="0" cellpadding="7" cellspacing="0" width="100%" summary=
"header">
<tr>
<td valign="top" width="300">
<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
"C++ Boost" src="../../../../c++boost.gif" border="0"></a></h3>
<td valign="top">
<h1 align="center">Boost.Python</h1>
<h2 align="center">Header &lt;boost/python/to_python_indirect.hpp&gt;</h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#introduction">Introduction</a>
<dt><a href="#classes">Classes</a>
<dd>
<dl class="page-index">
<dt><a href="#to_python_indirect-spec">Class Template <code>to_python_indirect</code></a>
<dd>
<dl class="page-index">
<dt><a href="#to_python_indirect-spec-synopsis">Class Template
<code>to_python_indirect</code> synopsis</a>
<dt><a href="#to_python_indirect-spec-observers">Class Template
<code>to_python_indirect</code> observer functions</a>
<dt><a href="#to_python_indirect-spec-statics">Class Template
<code>to_python_indirect</code> static functions</a>
</dl>
</dl>
<dt><a href="#examples">Example</a>
</dl>
<hr>
<h2><a name="introduction"></a>Introduction</h2>
<code>&lt;boost/python/to_python_indirect.hpp&gt;</code> supplies
a way to construct new Python objects that hold wrapped C++ class
instances via a pointer or smart pointer.
<h2><a name="classes"></a>Classes</h2>
<h3><a name="to_python_indirect-spec"></a>Class template <code>to_python_indirect</code></h3>
<p>Class template <code>to_python_indirect</code> converts objects
of its first argument type to python as extension class instances, using the ownership policy provided by its 2nd argument.
<p>
<table border="1" summary="to_python_indirect template parameters">
<caption>
<b><code>to_python_indirect</code> Requirements</b><br>
In the table below, <b><code>x</code></b> denotes an object of
type <code>T</code>, <b><code>h</code></b> denotes an
object of type
<code>boost::python::objects::instance_holder*</code>, and
<b><code>p</code></b> denotes an object of type
<code>U*</code>.
</caption>
<tr>
<th>Parameter
<th>Requirements
<th>Description
<tr>
<td><code>T</code>
<td>Either <code>U</code>&nbsp;<i>cv</i><code>&amp;</code>
(where <i>cv</i> is any optional cv-qualification) or a <a
href="Dereferenceable.html">Dereferenceable</a> type such that
<code>*x</code> is convertible to <code>U const&amp;</code>, where
<code>U</code> is a class type.
<td>A type deferencing a C++ class exposed to Python using
class template <code><a
href="class.html#class_-spec">class_</a></code>.
<tr>
<td><code>MakeHolder</code>
<td>h = MakeHolder::execute(p);
<td>A class whose static <code>execute()</code> creates an
<code>instance_holder</code>.
</table>
Instantiations of <code>to_python_indirect</code> are models of <a
href="ResultConverter.html#ResultConverter-concept">ResultConverter</a>.
<h4><a name="to_python_indirect-spec-synopsis"></a>Class template <code>to_python_indirect</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class T, class MakeHolder&gt;
struct to_python_indirect
{
static bool convertible();
PyObject* operator()(T ptr_or_reference) const;
private:
static PyTypeObject* type();
};
}}
</pre>
<h4><a name="to_python_indirect-spec-observers"></a>Class template <code>to_python_indirect</code> observers</h4>
<pre>
PyObject* operator()(T x) const;
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>x</code> refers to an object (if it
is a pointer type, it is non-null). <code>convertible() ==
true</code>.
<dt><b>Effects:</b> Creates an appropriately-typed Boost.Python
extension class instance, uses <code>MakeHolder</code> to create
an <code>instance_holder</code> from <code>x</code>, installs
the <code>instance_holder</code> in the new extension class
instance, and returns a pointer to it.
</dl>
<h4><a name="to_python_indirect-spec-statics"></a>Class template <code>to_python_indirect</code> statics</h4>
<pre>
bool convertible();
</pre>
<dt><b>Effects:</b> Returns <code>true</code> iff any module has
registered a Python type corresponding to <code>U</code>.
<h2><a name="examples"></a>Example</h2>
This example replicates the functionality of <a
href="reference_existing_object.html#reference_existing_object-spec">reference_existing_object</a>,
but without some of the compile-time error checking.
<pre>
struct make_reference_holder
{
typedef boost::python::objects::instance_holder* result_type;
template &lt;class T&gt;
static result_type execute(T* p)
{
return new boost::python::objects::pointer_holder&lt;T*, T&gt;(p);
}
};
struct reference_existing_object
{
// metafunction returning the <a href="ResultConverter.html#ResultConverter-concept">ResultConverter</a>
template &lt;class T&gt;
struct apply
{
typedef boost::python::to_python_indirect&lt;T,make_reference_holder&gt; type;
};
};
</pre>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
16 February, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>

View File

@@ -1,101 +0,0 @@
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<title>Boost.Python - &lt;boost/python/to_python_value.hpp&gt;</title>
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<h3><a href="../../../../index.htm"><img height="86" width="277" alt=
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<h1 align="center">Boost.Python</h1>
<h2 align="center">Header
&lt;boost/python/to_python_value.hpp&gt;</h2>
</table>
<hr>
<h2>Contents</h2>
<dl class="page-index">
<dt><a href="#classes">Classes</a>
<dd>
<dl class="page-index">
<dt><a href="#to_python_value-spec">Class
<code>to_python_value</code></a>
<dd>
<dl class="page-index">
<dt><a href="#to_python_value-spec-synopsis">Class template
<code>to_python_value</code> synopsis</a>
<dt><a href="#to_python_value-spec-observers">Class template
<code>to_python_value</code> observer functions</a>
</dl>
</dl>
</dl>
<hr>
<h2><a name="classes"></a>Classes</h2>
<h3><a name="to_python_value-spec"></a>Class template
<code>to_python_value</code></h3>
<p><code>to_python_value</code> is a model of <a href=
"ResultConverter.html#ResultConverter-concept">ResultConverter</a>
which copies its argument into a new Python object.
<h4><a name="to_python_value-spec-synopsis"></a>Class
<code>to_python_value</code> synopsis</h4>
<pre>
namespace boost { namespace python
{
template &lt;class T&gt;
struct to_python_value
{
typedef typename <a href="../../../type_traits/index.htm#transformations">add_reference</a>&lt;
typename <a href="../../../type_traits/index.htm#transformations">add_const</a>&lt;T&gt;::type
&gt;::type argument_type;
static bool convertible();
PyObject* operator()(argument_type) const;
};
}}
</pre>
<h4><a name="to_python_value-spec-observers"></a>Class
<code>to_python_value</code> observers</h4>
<pre>
static bool convertible();
</pre>
<dl class="function-semantics">
<dt><b>Returns:</b> <code>true</code> iff a converter has been registered which can convert <code>T</code> to python by-value.
</dl>
<pre>
PyObject* operator()(argument_type x) const;
</pre>
<dl class="function-semantics">
<dt><b>Requires:</b> <code>convertible()&nbsp;==&nbsp;true</code>
<dt><b>Effects:</b> converts <code>x</code> to python
<dt><b>Returns:</b> the resulting Python object iff a converter for <code>T</code> has been registered, <code>0</code> otherwise.
</dl>
<p>Revised
<!--webbot bot="Timestamp" S-Type="EDITED" S-Format="%d %B, %Y" startspan -->
15 February, 2002
<!--webbot bot="Timestamp" endspan i-checksum="39359" -->
<p><i>&copy; Copyright <a href="../../../../people/dave_abrahams.htm">Dave
Abrahams</a> 2002. All Rights Reserved.</i>

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