Windows Python C extension only works with my own Python build (32-bit build using VC++ 2008 Express)

Question

I am trying to build a simple Python wrapper for a library we are using. But the weird thing is this extension doesn't work with the official Python build, only with my own Python build. Even though they were based on the same version of source code. I am also a C/C++ rookie so I am not sure if my program is correct or not.

So one of the method I am trying to wrap is like this (copied from their SDK document):

Syntax

void IoWrite(IOHANDLE hIo, void * sourceBuffer, long size);

Parameters

hIo The handle to the IO signal, i.e. the return value from the IoConnect operation.

sourceBuffer The parameter containing the value that the IO signal should have.

size The size of the signal to write.

Return value

No return value used.

Code Example

IOHANDLE hIoSig;
long ioVariable = 10;

hIoSig = IoConnect("IoSigName", sizeof(ioVariable));
IoWrite(hIoSig, &ioVariable, sizeof(ioVariable));

Here is the Python extension:

#include "Python.h"
#include <conio.h>
#include "SimIoPort.h"

static PyObject *
ex_IoWrite(PyObject *self, PyObject *args)
{
char *IoPortName;
long PortValue;
IOHANDLE hIOsignal;

if (!PyArg_ParseTuple(args, "si", &IoPortName, &PortValue))
{
    return NULL;
}

hIOsignal = IoConnect(IoPortName, sizeof(PortValue));
IoWrite(hIOsignal, &PortValue, sizeof(PortValue));

Py_INCREF(Py_None);
return Py_None;
}

static PyMethodDef SimIo_methods[] = {
    {"io_write", ex_IoWrite, METH_VARARGS,
    "IoWrite method."},
    {NULL, NULL, 0, NULL}
};

PyMODINIT_FUNC
initSimIo(void)
{
    Py_InitModule("SimIo", SimIo_methods);
}

Here is my setup.py:

from distutils.core import setup, Extension

simio_module = Extension('SimIo',
                        include_dirs = ['Headers', 'Libs'],
                        libraries = ['user32', ],
                        sources = ['SimIoModule.c', 'Libs\SimIoPort.c'],
                        )


setup(name = "SimIo",
    version = "0.1",
    description = "SimIo",
    ext_modules = [simio_module],
)

If I use the official Python build 2.7.5, it will crash some other applications that use this SDK, but I don't have problem if I use it with my own Python 2.7.5 built with VS 2008 Express.

Thanks a lot!

Additional information regarding to the compiler: I was using MS Visual C++ 2008 Express Edition with SP1, nothing else.

my compiler setup

Compiled using "C:\Python27\python.exe setup.py build" My compiler output

Can you describe how you built your extension. Which SDK are you linking against? How are you linking the runtime? — David Heffernan, Nov 01 '13 at 11:02
@DavidHeffernan Hi! I was using Visual C++ 2008 Express with SP1. — Zhe Li, Nov 01 '13 at 11:24
Yes. Which SDK are you linking against? How are you linking the runtime? — David Heffernan, Nov 01 '13 at 11:27
Did you run setup.py with your Python build? Try running it with official Python. — Janne Karila, Nov 01 '13 at 13:48
@DavidHeffernan I think it's MS VC9.0 32bit. I don't really know how I linked it:P I just ran "python setup.py build". — Zhe Li, Nov 01 '13 at 13:57
@JanneKarila actually I was using the official build when running setup.py:( — Zhe Li, Nov 01 '13 at 13:59

score 0 · Answer 1 · answered Nov 01 '13 at 10:54

Building from the same source code is probably not enough. All Python modules are loaded into a single process. This means that the base Python and all modules have to be compiled with more or less the same compilation parameters. Compiler options that change how the code behaves could have an impact on the binary compatibility of the compiled code with other compilations. Also, different compiler versions (or different compilers) may need different compiler options to generate compatible code. Some of those factors (the compiler, the compiler version, the compiler options used) might or might not be changed without getting into trouble. If you don't want to spend lots of time and energy to get to know which factors are important, it's usually best to use the same compiler, the same compiler version, with exactly the same compiler options. Now you can achieve that with compiling everything yourself (and possibly staying incompatible with the official build), or setting up exactly the same environment as used for the official build.

Windows Python C extension only works with my own Python build (32-bit build using VC++ 2008 Express)

1 Answers1