ctypes

lib.c

/* sum of a list of doubles */

double sum(double *data, int n)

{

  int i=0;

  double sum=0.0;

  for (i=0; i<n; i++)

  {

  sum += data[i];

  }

  return sum;

}

/* mean of a list of doubles */

double mean(double *data, int n)

{

  double s = sum(data, n);

  return s/((double)n);

}

gcc -shared -fPIC lib.c -o lib.so

test.py

from ctypes import *

so = cdll.LoadLibrary("/home/barnix/py/ctypes/ex1/lib.so")

# Set up interfaces

so.mean.argtypes= [POINTER(c_double), c_int]

so.mean.restype = c_double

so.sum.argtypes = [POINTER(c_double), c_int]

so.sum.restype = c_double

# Call the functions.

def cmean(dlist):

  doubleArray = c_double*len(dlist) # Data Type (double[n])

  cx = doubleArray(*dlist) # Actual array

  n = len(cx) # Length of the data

  result = so.mean(cx, n)

  return float(result)

def csum(dlist):

  doubleArray = c_double*len(dlist)

  cx = doubleArray(*dlist)

  n = len(cx)

  result = so.sum(cx, n)

  return float(result)

# We can now use the functions as if they were pure python!

data = [1,2,3,4,5,6]

print cmean(data)

print csum(data)

#((void *) -1)

print c_void_p(-1).value