setting a C-structure from Python

[tidop at my-deja.com]

My aim is to write an extension module to access functions in C which "get"
and "set" some structures from/in shared memory.

In order to do this, I implemented the following programs:
*    structure.py
*    test_API.c

 It works well when I set the structure the first time, but not a second time
I have got the following (run-time) error... where is the bug ?


>>> import structure
The structure is now:
name Benoit
age 22
rate 3.141500


Traceback (innermost last):
  File "<stdin>", line 1, in ?
  File "structure.py", line 19, in ?
    test_API.setstruct(packed)
TypeError: argument 1: expected string,
                                         found




I am working with Python 1.5.2 on QNX 4.25 test_API.c  is therefore
statically linked with Python as dynamic linking is not possible on QNX.



file : structure.py
-----------------------------------------

import struct
import test_API

#1st  try
fmt="20sif"
a="Benoit"
b=22
c=3.1415
packed=struct.pack(fmt,a,b,c)
test_API.setstruct(packed)

#2nd try
a="Ben"
b=23
c=3.1417
packed=struct.pack(fmt,a,b,c)
test_API.setstruct(packed)


file: test_API.c
--------------------------------------
#include <stdio.h>
#include "Python.h"

typedef struct{
	char 	name[20];
	int 	age;
	float 	rate;
} examplestruct;


examplestruct * example;


static void 	print_struct()
{
	printf("The structure is now: \n");
	printf("name %s\n",example->name);
	printf("age %i\n",example->age);
	printf("rate %f\n", example->rate);
}


static PyObject * test_setstruct(PyObject * self, PyObject * args)
{
	PyObject * string_from_python;

	if (!PyArg_ParseTuple(args,"S",&string_from_python)) return NULL;

	example= (examplestruct *) PyString_AsString(string_from_python);
	Py_DECREF(string_from_python);
	print_struct();

	Py_INCREF(Py_None);
	return Py_None;
}


static PyObject * test_getstruct(PyObject * self, PyObject * args)
{
	/* if there are any arguments */
	if (!PyArg_NoArgs(args))
		return NULL;
	return PyString_FromString(example);
}


/*************************************************************
	METHOD REGISTRATION TABLE
	List of functions defined in the module
*************************************************************/
static struct PyMethodDef test_API_methods[] = {
	{"setstruct",	test_setstruct, 1},
	{"getstruct",	test_getstruct, 1},
	{NULL,		NULL}
};

/*************************************************************
	Initialization function
*************************************************************/
void inittest_API()
{
		PyObject *m, *d;

		/*create the module and add the functions */
		m= Py_InitModule("test_API", test_API_methods);

		/* add symbolic constants to the module */
		d= PyModule_GetDict(m);

		if (PyErr_Occurred())
			Py_FatalError("can't initialize module test_API\n");
}



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