Integrating Python + C: Ctypes and Cython

demo.py

import ctypes
import time
import numpy as np
import example_cython


def mult_sum(a):
    b = 0
    for i in range(10000):
        b += a * i
    return b


def mult_sum_np(a):
    return np.sum(np.arange(10000) * a)


def evaluate(name, func):
    st = time.time()
    out = [func(x) for x in range(10)]
    print('%s[%f]' % (name, time.time() - st))
    return out


def main():
    example = ctypes.cdll.LoadLibrary('example.so')

    out = evaluate('Ctypes', example.mult_sum_c)
    out2 = evaluate('Python', mult_sum)
    out3 = evaluate('numpy', mult_sum_np)
    out4 = evaluate('Cython', example_cython.mult_sum)
    assert out == out2 == out3 == out4


if __name__ == '__main__':
    main()

example.c

#include "example.h"
int mult_sum_c(int a) {
    int i;
    int b = 0;
    for (i = 0; i < 10000; ++i) {
        b += a * i;
    }
    return b;
}

example.h

#ifndef EXAMPLE_H
#define EXAMPLE_H
int mult_sum_c(int a);
#endif

example_cython.pyx

cdef extern from "example.h":
    int mult_sum_c(int)


def mult_sum(int a):
    return mult_sum_c(a)
    

run.sh

gcc -O2 --shared example.c -o example.so
cython example_cython.pyx
gcc -shared -pthread -fPIC -fwrapv -O2 -Wall -fno-strict-aliasing -I `python -c "import distutils.sysconfig;print distutils.sysconfig.get_python_inc()"` -o example_cython.so example_cython.c example.so
LD_LIBRARY_PATH="." python demo.py