File objects in extension module

[Mike Steed]

Hi,

I am trying to use a file object passed from Python to a C extension
module (Windows 98).  All the C runtime calls crash when I pass them the
FILE pointer (fwrite, fflush, etc.)

The pointer I get back from PyFile_AsFile seems okay -- the struct
members have reasonable values, etc.

I have seen the same behavior with MS VC++ (4.2) and egcs/mingw32
(1.1.2), and with Python-1.5.1 and 1.5.2b2.

What am I missing?

Here is a minimal code snippet, without the error checking code:

----- example.c
#include "Python.h"

static PyObject *
ex_flush(PyObject *self, PyObject *args)
{
   PyObject *file;

   /* ... code to check arg count and types removed ... */

   file = PyTuple_GetItem(args, 0);
   fflush(PyFile_AsFile(file));

   Py_INCREF(Py_None);
   return Py_None;
}

static PyMethodDef example_methods[] = {
   {"flush", ex_flush, 1},
   {NULL, NULL}
};

void
initexample()
{
   Py_InitModule("example", example_methods);
}


----- on the Python side:
>>> import example
>>> f = open('test', 'w')
>>> example.flush(f)      --> crash!


Puzzled,
Mike