extending python to C

[Edward Tsang]

Hey, I am trying to initialise a C structure from Python.My Aim is to
init a C structure without passing each indivual elementsthrough the
interface, but rather package the whole thing and pass that in one
time. Then the C may do somethign about it, initialise its wonstruct
and pass back a struct with the same kind of elements but withdifferent
parameters. I am stuck with the intialising the C structpart, and have
not clue how to convert the C struct back to a PyObjectappropriate to
pass back to the Python script. Please help . I have also tried
replacing string_from_Pythong to be a PyStringObejct*, segmentation
falt persisits.
ANY THOUGHTS????? ANY OPIONS???
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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