Sample that describe how to call c function from python, and how to give float array.

Makefile

PYTHON_VERSION=2.7
CCFLAG=-std=gnu99 -Wall -fPIC -I/usr/include/python${PYTHON_VERSION}
LDFLAG=-lpython${PYTHON_VERSION}

run: build
	python -m unittest pythonc_test
build: spam.so

spam.so: spam.o
	gcc -shared -o $@ $^ ${LDFLAG}
.c.o:
	gcc -c ${CCFLAG} $^
clean:
	rm -f spam.o spam.so

pythonc_test.py

import unittest
import spam

class PythonCTest(unittest.TestCase):
    def test(self):
        self.assertEquals(6, spam.sum(3, [1, 2, 3]))

if __name__ == '__main__':
    unittest.main()

spam.c

#include<Python.h>

static float* create_array(PyObject*);
static void dispose_array(float*);

static PyObject *
sum(PyObject *self, PyObject *args)
{
    int num;
    PyObject *obj;
    float sum = 0;

    if (!PyArg_ParseTuple(
                args, "iO!",
                &num,
                &PyList_Type, &obj)) {
        return NULL;
    }
    float* a = create_array(obj);

    for (int i=0; num > i; ++i) {
        sum += a[i];
    }

    dispose_array(a);

    return Py_BuildValue("f", sum);
}

static float* create_array(PyObject* listObj) {

    int numLines = PyList_Size(listObj);
    if (numLines < 0)   return NULL;
    float *result = (float*)malloc(sizeof(float) * numLines);

    for (int i=0; i<numLines; i++){
        PyObject *obj = PyList_GetItem(listObj, i);
        result[i] = (float)(PyFloat_AsDouble(obj));
    }

    return result;

}

static void dispose_array(float* a) {
    free(a);
}

static PyMethodDef methods[] = {
    {"sum", (PyCFunction)sum, METH_VARARGS, "calculate sum.\n"},
    {NULL, NULL, 0, NULL}
};

void initspam(void)
{
    Py_InitModule3("spam", methods, "");
}