I'm writing an extension module in C in which I'm passing an array of
floats from C to python. The code below illustrates a simple C
function designed to output an array of floats.
---------
extTest.c
---------
#include <stdio.h>
double *testArray(int nsamp) {
double nums[10000];
int i;
double cumdata = 0.0;
printf("%d\n", nsamp);
for (i=0; i<=nsamp; i++) {
printf("%d\n", i);
nums[i] = cumdata;
cumdata += 0.5;
printf("%f\n", nums[i]);
}
return nums;
}
Then I write a wrapper function to pass the data back and forth between
C and Python.
----------------
extTestWrapper.c
----------------
#include "/usr/include/python2.4/Python.h"
#include <stdio.h>
// external declarations
extern float *testArray(int);
// Python wrapper for the testArray function
PyObject *extTest_testArray(PyObject *self, PyObject *args) {
double *nums;
int nsamp;
int i;
PyObject *pynums;
if (!PyArg_ParseTuple(args, "i", &nsamp)) {
return NULL;
}
// call the C function
nums = testArray(nsamp);
// build a Python list object containing the array values
pynums = PyList_New(nsamp);
for (i=0; i<=nsamp; i++){
PyList_SetItem(pynums, i, PyFloat_FromDouble(nums[i]));
}
return Py_BuildValue("O", pynums);
}
// method table mapping names to wrappers
static PyMethodDef extTestMethods [] = {
{"testArray", extTest_testArray, METH_VARARGS},
{NULL, NULL}
};
//module init function
void initextTest() {
Py_InitModule("extTest", extTestMethods);
}
I then run the following setup.py script using python setup.py install
--install-lib=.
--------------------------------------------------------------------------------------------
# setup.py for extTest
from distutils.core import setup, Extension
setup(name="extTest", version="0.0.1",
ext_modules=[Extension("extTest", ["extTest.c", "extTestWrapper.c"])])
--------------------------------------------------------------------------------------------
The library builds and installs ok. When I invoke the testArray
function, it appears to work correctly (the output is as expected).
For example,
import extTest
a = extTest.testArray(5)
yields the following output:
5
0
0.000000
1
0.500000
2
1.000000
3
1.500000
4
2.000000
5
2.500000
Exception exceptions.IndexError: 'list assignment index out of range'
in 'garbage collection' ignored
Fatal Python error: unexpected exception during garbage collection
Aborted
Here is where I'm stumped. I must be doing something wrong during the
PyList_SetItem or the Py_BuildValue.
Any ideas on fixing this problem ?
Regards,
Rimmer
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