Why is PyObject_Print crashing?

Question

I've been playing with the Python 3.3 C-API to see if I could possibly use it in a planned upcoming project, and almost immediately ran into problems.

Even code this simple crashes with 0xc0000005 as the return:

#include <Python.h>
#include <cstdio>

int main(){
    Py_Initialize();

    Py_IncRef(Py_True); //just in case?
    PyObject_Print(Py_True,stdout,Py_PRINT_RAW);
    Py_DecRef(Py_True);

    Py_Finalize();
    return 0;
}

Testing shows PyObject_Print is generating the crash. What's wrong with this code and/or my setup?

Answer 1

This is most probably due to incorrect linkage. The crash is common when the File* in your code is different from the File* in the python lib you linked against. This can happen when the libraries liked against have been compiled by a different compiler or different version of the compiler, that uses a different runtime.

Answer 2

I've had PyObject_Print() crashing when i moved a C module from Pyhton 2.x -> 3.x

First off, check the MS VS version (MSC) in your C module matches the version reported by Python.

For example, running python.exe reports: Python 3.3.2 (v3.3.2:d047928ae3f6, May 16 2013, 00:03:43) [MSC v.1600 32 bit (Intel)] on win32

Add an fprintf to your module's init function:

fprintf(stderr, "C - MSC_VER %d\n", _MSC_VER);

giving:

C - MSC_VER 1600

Secondly, check your command line options. Again, the commands for my simple test module were:

cl.exe /Fosmod.obj /c /I "%INCLUDE%" /I c:\python33\include smod.c link.exe /dll /out:smod.pyd smod.obj /LIBPATH:c:\python33\libs

These caused my module to crash in PyObject_Print()!

A quick read of the 'cl' command line options and I added '/MD':

cl.exe /MD /Fosmod.obj /c /I "%INCLUDE%" /I c:\python33\include smod.c link.exe /dll /out:smod.pyd smod.obj /LIBPATH:c:\python33\libs

Fixed!