<br><br><div class="gmail_quote">2009/12/8 Jadhav, Alok <span dir="ltr"><<a href="mailto:alok.jadhav@credit-suisse.com">alok.jadhav@credit-suisse.com</a>></span><br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
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<p><font face="Arial" size="2">I am using SWIG to extend Python to C++.</font> <font face="Arial" size="2"></font> <font face="Arial" size="2"> But the questions I have consists of basic Python C API related. I hope this list will be able to help me. </font></p>
<p><font face="Arial" size="2">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.</font></p>
<p><font face="Arial" size="2">Background</font>
<br><font face="Arial" size="2">-----------</font>
</p>
<p><font face="Arial" size="2">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).</font></p>
<p><font face="Arial" size="2">Issue</font>
<br><font face="Arial" size="2">-----</font>
<br><font face="Arial" size="2">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.</font></p>
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<p><font face="Arial" size="2">Some code snippets</font>
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</p>
<p><font face="Arial" size="2">C++ function which calls python function. ... </font>
</p>
<p><font face="Arial" size="2">[code]</font>
<br><font face="Arial" size="2">static void PythonCallBack(RFAMessage *msg, void *clientdata)</font>
<br><font face="Arial" size="2">{</font>
<br><font face="Arial" size="2"> PyObject *func, *arglist;</font>
<br><font face="Arial" size="2"> int blah = 1;</font>
<br><font face="Arial" size="2"> </font>
<br><font face="Arial" size="2"> PyGILState_STATE state; </font>
<br><font face="Arial" size="2"> state = PyGILState_Ensure();</font>
<br><font face="Arial" size="2"> func = (PyObject *) clientdata; // Get Python function</font>
<br><font face="Arial" size="2"> RFAMessageWrapper msg2(msg);</font>
<br> <font face="Arial" size="2">try {</font>
<br> <font face="Arial" size="2">arglist = Py_BuildValue("(O)",msg2); // Build argument list</font>
<br></p></div></blockquote><div>This is bad. <font face="Arial" size="2">Py_BuildValue("(O)",</font> is expecting to find a PyObject, but <font face="Arial" size="2">msg2 is not a PyObject.<br><br>Additionally, PyObjects must be created with PyObject_New, and never stack allocated like msg2 is.<br>
</font><br>I cannot offer any solution, as it would be SWIG specific and I am not familiar with SWIG.<br> </div><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">
<div><p> <font face="Arial" size="2">//arglist = Py_BuildValue("(i)", blah);</font>
<br> <font face="Arial" size="2">PyEval_CallObject(func,arglist); // Call Python</font>
<br> <font face="Arial" size="2">} catch (...) {</font>
<br> <font face="Arial" size="2">cout<<"Unknown exception..."<<endl;</font>
<br> <font face="Arial" size="2">}</font>
<br><font face="Arial" size="2"> Py_XDECREF(arglist); // Trash arglist</font>
<br><font face="Arial" size="2"> PyGILState_Release(state); </font>
<br><font face="Arial" size="2">}</font>
<br><font face="Arial" size="2">[/code]</font>
</p>
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<p><font face="Arial" size="2">Python function call..</font>
</p>
<p><font face="Arial" size="2">[code]</font>
<br><font face="Arial" size="2">def callback_fun(msg):</font>
<br><font face="Arial" size="2"> try:</font>
<br><font face="Arial" size="2"> print "RFAMessage received for service:"+msg.service</font>
<br><font face="Arial" size="2"> except Exception:</font>
<br><font face="Arial" size="2"> print "Exception handled"</font>
<br><font face="Arial" size="2">[/code]</font>
</p>
<p><font face="Arial" size="2">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.</font></p>
<p><font face="Arial" size="2">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</font> <font face="Arial" size="2">exception</font><font face="Arial" size="2">.</font></p>
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<p><font face="Arial" size="2">I have spent long time to solve this issue but in vain. I hope I get some help from this Forum.</font>
</p>
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<p><font face="Arial" size="2">Regards, </font>
<br><font face="Arial" size="2">Alok<span lang="ja"></span></font>
</p>
</div>
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