Maybe I missed something, but I think this should work for you: class_<A, A*, boost::noncopyable> classA("A", noinit);// this is the class object - only one registration! classA.def("f1", &A::f1) .... ; CPPObj cppObj; object instanceOfA1 = classA(&cppObj);// multiple instances object instanceOfA2 = classA(&cppObj); regards, max

-----Original Message----- From: Francois Ostiguy [mailto:ostiguy@fnal.gov] Sent: Friday, August 13, 2004 3:23 PM To: c++-sig@python.org Subject: [C++-sig] creating an instance of a class_<> object in c++ and exporting it to python

Hi -

I am try in to do the following:

Consider a C++ class A wrapped using boost.python:

class_<A, A*, boost::noncopyable>("A", noinit) .def("f1", &A::f1) .... ;

...

From C++, I would like to

(1) create an instance of a wrapped object "A", initializing it using a pointer to an existing instance of a C++ A object.

(2) export the python object into the namespace of an (embedded) interpreter.

AFAIK boost.python does not provide a mechanism to accomplish (2), but that seems straightforward using the Python C-API.

I am really at a loss on how to achieve (1) using boost.python. It would seem like a useful thing to create instances of wrapped objects in C++. The most relevant bit of information I found is in the tutorial:

...

Due to the dynamic nature of Boost.Python objects, any class_<T> may also be one of these types! The following code snippet wraps the class (type) object.

...

We can use this to create wrapped instances. Example object vec345 = ( class_<Vec2>("Vec2", init<double, double>()) .def_readonly("length", &Point::length) .def_readonly("angle", &Point::angle) )(3.0, 4.0);

assert(vec345.attr("length") == 5.0);

This code does create an instance of vec345; however, unless I misunderstand something I am under the impression that every invocation of class_<A> will re-register the class A. Perhaps this is not a problem; nevertheless it appears unnecessarily redundant and potentially error-prone (multiple class_<A> declarations appearing in different source files).

Is it possible to somehow retrieve the class type of an extended C++ class directly from the interpreter and then create a new instance ?

Any comments or insight would be most welcome.

-Francois

-------------------------------------------------------------- -------------- Dr. Jean-Francois OSTIGUY voice: (630) 840-2231 Beam Physics Dept MS220 FAX: (630) 840-6039 Fermi National Accelerator Laboratory email: ostiguy@fnal.gov Batavia IL 60510-0500 WWW:www-ap.fnal.gov/~ostiguy

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