extension_class<T> is a subclass of
PyTypeObject, the struct which Python's 'C' API uses
to describe a type. An obj of
the extension_class<> becomes the Python type
object corresponding to hello::world. When we add it to the module it goes into the
module's dictionary to be looked up under the name "world".
Py_cpp uses C++'s template argument deduction mechanism to determine the
types of arguments to functions (except constructors, for which we must
provide an argument list
because they can't be named in C++). Then, it calls the appropriate
overloaded functions PyObject*
to_python(S) and
S'from_python(PyObject*,
type<S>) which convert between any C++
type S and a PyObject*, the type which represents a
reference to any Python object in its 'C' API. The extension_class<T>
template defines a whole raft of these conversions (for T, T*,
T&, std::auto_ptr<T>, etc.), using the same inline
friend function technique employed by the boost operators
library.
Because the to_python and from_python functions
for a user-defined class are defined by
extension_class<T>, it is important that an instantiation of
extension_class<T> is visible to any code which wraps
a C++ function with a T, T*, const T&, etc. parameter or
return value. In particular, you may want to create all of the classes at
the top of your module's init function, then def the member
functions later to avoid problems with inter-class dependencies.
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© Copyright David Abrahams 2000. 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.
Updated: Sept 30, 2000