capi-sig December 2009

capi-sig@python.org

7 participants
6 discussions

Reference counts and dictionary creadtion

by Dan Colesworthy

Hello, I am attempting to write a python extension in C to "glue" the ASIO SDK to python 2.5.4. However I am really confused about reference counts. Below is a code snippet that "seems" to work, however I suspect that some of the object reference counts have been incremented too many times. static PyObject * getAsioInfo(PyObject *self, PyObject *args) { PyObject *dict = Py_None; if (loadAsioDriver (ASIO_DRIVER_NAME)) { if (ASIOInit (&asioDriverInfo.driverInfo) == ASE_OK){ dict = PyDict_New(); PyDict_SetItem(dict, PyString_FromString("asioVersion"), PyInt_FromLong(asioDriverInfo.driverInfo.asioVersion) ); PyDict_SetItem(dict, PyString_FromString("driverName"), PyString_FromString(asioDriverInfo.driverInfo.name) ); return dict; } } return Null; } As nearly as I can tell from the Python source code, PyDict_SetItem will do a Py_INCREF on both the key and value parameters. However, it looks as if PyInt_FromLong will incref the object it is returning - at least if it is a "small value". Am I on the right track here? Or am I better off doing something like: PyObject *str, *lng; str = PyString_FromString("asioVersion"); lng = PyInt_FromLong(asioDriverInfo.driverInfo.asioVersion) ); PyDict_SetItem(dict, str, lng); Py_DECREF(str); Py_DECREF(lng); Thanks in advance for all advice! Dan Colesworthy

10 years, 8 months

ANN: PyBindGen 0.13 released

by Gustavo Carneiro

PyBindGen is a Python module that is geared to generating C/C++ code that binds a C/C++ library for Python. It does so without extensive use of either C++ templates or C pre-processor macros. It has modular handling of C/C++ types, and can be easily extended with Python plugins. The generated code is almost as clean as what a human programmer would write. It can be downloaded from: http://code.google.com/p/pybindgen/ Bug reports should be filed here: https://bugs.launchpad.net/ <https://bugs.launchpad.net/pybindgen> pybindgen <https://bugs.launchpad.net/pybindgen> <https://bugs.launchpad.net/pybindgen>Documentation: http://packages.python.org/PyBindGen/ NEWS: - Lots of small bug fixes - Custodian/ward-style memory management works better now - Add 'reference_existing_object' and 'return_interal_reference' options for pointer/reference return values - New Sphinx based documentation -- Gustavo J. A. M. Carneiro INESC Porto, Telecommunications and Multimedia Unit "The universe is always one step beyond logic." -- Frank Herbert

10 years, 9 months

Using the Python/C API with mingw-w64

by Nathan Osman

I am having a little bit of trouble getting the Python headers working with mingw-w64. The app I'm developing is C++ based and is being compiled for the x64 platform. When I include Python headers I get errors saying that standard C functions like round() are being redefined. I think it was in PyMath.h. And yes, I am using the 64 bit headers and libs from python.org - George _________________________________________________________________ Windows Live: Keep your friends up to date with what you do online. http://go.microsoft.com/?linkid=9691815

10 years, 9 months

Re: [capi-sig] Python C Api extension (multi threaded environment) Raises exception (Accesss violation error)

by Stefan Behnel

Jadhav, Alok, 08.12.2009 01:09: > 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). This might help: http://www.linuxjournal.com/article/3641 Stefan

10 years, 9 months

Re: [capi-sig] Python C Api extension (multi threaded environment) Raises exception (Accesss violation error)

by Ulf Worsoe

Hi, I don't have any experience with SWIG, but I can see two places where things may go wrong: 1) If the call back function was garbage collected before you called it (probably not the case if it is a normal function on the Python side) 2) I assume that RFAMessageWrapper is an extension of a PyObject that swig generated; in this case you should probably build arglist using a pointer to, ie: arglist = Py_BuildValue("(O)",&msg2); -- Ulf Worsøe Mosek ApS On Tue, Dec 8, 2009 at 1:09 AM, Jadhav, Alok <alok.jadhav(a)credit-suisse.com> wrote: > 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 > > =============================================================================== > Please access the attached hyperlink for an important electronic communications disclaimer: > http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html > =============================================================================== > > _______________________________________________ > capi-sig mailing list > capi-sig(a)python.org > http://mail.python.org/mailman/listinfo/capi-sig >

10 years, 9 months

Python C Api extension (multi threaded environment) Raises exception (Accesss violation error)

by Jadhav, Alok

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 =============================================================================== Please access the attached hyperlink for an important electronic communications disclaimer: http://www.credit-suisse.com/legal/en/disclaimer_email_ib.html ===============================================================================

10 years, 9 months

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capi-sig December 2009