I am using SWIG to extend Python to C++. But the questions I have consists of basic Python C API related. I hope this list will be able to help me.

I am trying to solve a simple problem which many of you must have encountered. I wonder what I am doing different than others that I am facing a problem.

Background

A c++ library is wrapped in my C++ Class. This new C++ class is extended in Python using SWIG. I have to call a python function from C++ code ( which is on a new thread spawned from C++ main thread).

Issue

I am able to call the function. No issues. I could pass basic data types such as int. No issues. But when I try to pass a C++ class object (eg RFAMessageWrapper) to my python function I get an exception. It is an Access violation exception. The memory could not be "read". I am not even able to catch this exception.

Some code snippets

C++ function which calls python function. ...

[code] static void PythonCallBack(RFAMessage *msg, void *clientdata) { PyObject *func, *arglist; int blah = 1;

PyGILState_STATE state; state = PyGILState_Ensure(); func = (PyObject *) clientdata; // Get Python function RFAMessageWrapper msg2(msg); try { arglist = Py_BuildValue("(O)",msg2); // Build argument list //arglist = Py_BuildValue("(i)", blah); PyEval_CallObject(func,arglist); // Call Python } catch (...) { cout<<"Unknown exception..."<<endl; } Py_XDECREF(arglist); // Trash arglist PyGILState_Release(state); } [/code]

Python function call..

[code] def callback_fun(msg): try: print "RFAMessage received for service:"+msg.service except Exception: print "Exception handled" [/code]

Whenever I try to access msg (of type RFAMessageWrapper .. C++ object) I get exception. msg is not None. I checked that in if condition. even type(msg) raises exception. RFAMessageWrapper class has been wrapped properly by SWIG as I could create an object manually and use it in Python. But only when I pass it from C++ to python I get this exception.

I have spent long time to solve this issue but in vain. I hope I get some help from this Forum.

Regards, Alok

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