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131 lines
3.7 KiB
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131 lines
3.7 KiB
HTML
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.0//EN"
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"http://www.w3.org/TR/REC-html40/strict.dtd">
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<title>
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A Simple Example
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</title>
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<div>
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<h1>
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<img width="277" height="86" id="_x0000_i1025" src="../../../c++boost.gif" alt=
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"c++boost.gif (8819 bytes)">
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</h1>
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<h1>
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A Simple Example
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</h1>
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<p>
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Suppose we have the following C++ API which we want to expose in
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Python:
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<blockquote>
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<pre>
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#include <string>
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namespace hello {
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class world
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{
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public:
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world(int);
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~world();
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std::string greet() const { return "hi, world"; }
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...
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};
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std::size_t length(const world& x) { return std::strlen(x.greet()); }
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}
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</pre>
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</blockquote>
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<p>
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Here is the C++ code for a python module called <code>hello</code>
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which exposes the API using:
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<blockquote>
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<pre>
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#include <boost/python/class_builder.hpp>
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// Python requires an exported function called init<module-name> in every
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// extension module. This is where we build the module contents.
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extern "C"
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#ifdef _WIN32
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__declspec(dllexport)
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#endif
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void inithello()
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{
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try
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{
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// create an object representing this extension module
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boost::python::module_builder m("hello");
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// Create the Python type object for our extension class
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boost::python::class_builder<hello::world> world_class(m, "world");
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// Add the __init__ function
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world_class.def(boost::python::constructor<int>());
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// Add a regular member function
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world_class.def(&hello::world::get, "get");
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// Add a regular function to the module
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m.def(hello::length, "length");
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}
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catch(...)
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{
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boost::python::handle_exception(); // Deal with the exception for Python
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}
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}
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// Win32 DLL boilerplate
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#if defined(_WIN32)
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#include <windows.h>
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extern "C" BOOL WINAPI DllMain(HINSTANCE, DWORD, LPVOID)
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{
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return 1;
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}
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#endif // _WIN32
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</pre>
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</blockquote>
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<p>
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That's it! If we build this shared library and put it on our <code>
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PYTHONPATH</code> we can now access our C++ class and function from
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Python.
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<blockquote>
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<pre>
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>>> import hello
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>>> hi_world = hello.world(3)
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>>> hi_world.greet()
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'hi, world'
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>>> hello.length(hi_world)
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9
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</pre>
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</blockquote>
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<p>
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We can even make a subclass of <code>hello.world</code>:
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<blockquote>
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<pre>
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>>> class my_subclass(hello.world):
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... def greet(self):
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... return 'hello, world'
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...
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>>> y = my_subclass(4)
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>>> y.greet()
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'hello, world'
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</pre>
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</blockquote>
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<p>
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Pretty cool! You can't do that with an ordinary Python extension type!
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<blockquote>
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<pre>
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>>> hello.length(y)
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9
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</pre>
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</blockquote>
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<p>
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Of course, you may now have a slightly empty feeling in the pit of
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your little pythonic stomach. Perhaps you feel your subclass deserves
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to have a <code>length()</code> of <code>12</code>? If so, <a href=
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"overriding.html">read on</a>...
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<p>
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Next: <a href="overriding.html">Overridable virtual functions</a>
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Previous: <a href="comparisons.html">Comparisons with other systems</a> Up:
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<a href="index.html">Top</a>
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<p>
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© Copyright David Abrahams 2000. Permission to copy, use, modify,
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sell and distribute this document is granted provided this copyright
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notice appears in all copies. This document is provided "as is" without
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express or implied warranty, and with no claim as to its suitability
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for any purpose.
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<p>
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Updated: Nov 26, 2000
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</div>
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