[C++-sig] Re: creating an instance of a class_<> object in c+ + an d exporting it to python

[Francois Ostiguy]

Dave and Max -

Many thanks. With your suggestions, I am getting much closer ... but it is
not quite working yet.

Here is what I tried (in slightly simplified form):


...

class A;

class_<A, A*, boost::noncopyable> PythonTypeA;

A* aptr = new A();

A* get_existing() { return aptr; }

object py_get_existing =
 make_function( &get_existing,
                return_value_policy<reference_existing_object>()  );

object PythonInstanceOfA  = PythonTypeA(  py_get_existing() );

...

The code compiles cleanly. Unfortunately, I get a core dump when the last
line is executed. The debugger tells me that the problem originates from
line 154 in return_from_python.hpp

151  inline T return_object_manager_from_python<T>::operator()(PyObject* obj) const
152   {
153       return T(
154           object_manager_traits<T>::adopt(expect_non_null(obj))
155           );
156   }
157 }
158
159 }}} // namespace boost::python::converter
160

obj is null and expect_non_null(obj) throws an exception. This function is
called from line 20 in object_call.cpp


13
14     template <BOOST_PP_ENUM_PARAMS_Z(1, N, class A)>
15     typename detail::dependent<object, A0>::type
16     operator()(BOOST_PP_ENUM_BINARY_PARAMS_Z(1, N, A, const& a)) const
17     {
18         typedef typename detail::dependent<object, A0>::type obj;
19         U const& self = *static_cast<U const*>(this);
20         return call<obj>(get_managed_object(self, tag), BOOST_PP_ENUM_PARAMS_Z(1, N, a));
21     }
22

so somehow, calling the object returned by py_get_existing appears
to return a null pointer.


-Francois

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