NEWBIE: init a C struct from Python easily -- problem

[ed_tsang at yahoo.com]

Hey, I am trying to initialise a C structure from Python.
My Aim is to init a C structure without passing each indivual elements
through the interface, but rather package the whole thing and pass that
it one time. Then the C may do somethign about it, initialise its won
struct and pass back a struct with the same kind of elements but with
different parameters. I am stuck with the intialising the C struct
part, and have not clue how to convert the C struct back to a PyObject
appropriate to pass back to the Python script. Please help . Below is
the code.

Error: segmentation fault occurres at
PyArg_ParseTuple(args,"s:mymath",string_from_Python))
PyString_Size(string_from_Python)calls inside
function pyfunc_mystruct

Here is what I tried:

>From the python script I have:
import struct
import mymath_wrapper
fmt = "120sf"
a=255
b='knights who say ni'
c=3.14159011841
data = struct.pack(fmt,a,b,c)
mymath_wrapper.mystruct(data)

in my mymath_wrapper.c file I have:
#include <Python.h>
#include "mymath.h"

PyObject*
pyfunc_mystruct(self, args)
 PyObject *self, *args;
 {
 PyObject* string_from_Python;
 if(!PyArg_ParseTuple(args,"s:mymath",string_from_Python))
 	return NULL;
 if(PyString_Size(string_from_Python)!= sizeof(struct diffstruct))
 {
 	PyErr_SetString(PyExc_AssertionError, "Given strgin not a good
size");
 	return NULL;
 }


 globaldiffstruct = (diffstruct *)PyString_AsString(string_from_Python);

 printf("globaldiffstruct calling within C:%d  %s %
f\n",globaldiffstruct->a, globaldiffstruct->b,globaldiffstruct->c);
 /* python side will print the last res value*/
 return string_from_Python; /* not correct, deal with this later */
 }

 static PyMethodDef mymathMethods[] =
 {
 	{"mystruct", pyfunc_mystruct, 1},
 	{NULL,NULL}
 };

 void initmymath_wrapper()
 {
 	(void) Py_InitModule("mymath_wrapper", mymathMethods);
 }


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