Question

Cython ships with a set of standard .pxd files that provide these declarations in a readily usable way that is adapted to their use in Cython. The main packages are cpython , libc and libcpp . The NumPy library also has a standard .pxd file numpy , as it is often used in Cython code. See Cython’s Cython/Includes/ source package for a complete list of provided .pxd files. (From http://docs.cython.org/src/tutorial/clibraries.html ).

Additional .pxd are also avaialbel for:

• The Rmath library
• The GNU scientific library

However, here is an example of how to write functions from an external C library if you have to do it yourself. The example is taken from https://github.com/cythonbook/examples and wraps the Mersenne Twister from http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/emt.html for use in Python.

if not os.path.exists('mt19937ar.h'):
    ! wget http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/CODES/mt19937ar.sep.tgz
    ! tar -xzvf mt19937ar.sep.tgz

--2015-03-26 16:02:41--  http://www.math.sci.hiroshima-u.ac.jp/~m-mat/MT/MT2002/CODES/mt19937ar.sep.tgz
Resolving www.math.sci.hiroshima-u.ac.jp... 133.41.16.48
Connecting to www.math.sci.hiroshima-u.ac.jp|133.41.16.48|:80... connected.
HTTP request sent, awaiting response... 200 OK
Length: 15433 (15K) [application/x-gzip]
Saving to: ‘mt19937ar.sep.tgz’

100%[======================================>] 15,433      37.3KB/s   in 0.4s

2015-03-26 16:02:42 (37.3 KB/s) - ‘mt19937ar.sep.tgz’ saved [15433/15433]

x mt19937ar.c
x mt19937ar.h
x mt19937ar.out
x mtTest.c
x readme-mt.txt

%%file mt.pxd

cdef extern from "mt19937ar.h":
    void init_genrand(unsigned long s)
    double genrand_real1()

Writing mt.pxd

%%file mt_random.pyx

cimport mt

def init_state(unsigned long s):
    mt.init_genrand(s)

def rand():
    return mt.genrand_real1()

Writing mt_random.pyx

%%file setup.py

from distutils.core import setup, Extension
from Cython.Build import cythonize

ext = Extension("mt_random",
                sources=["mt_random.pyx", "mt19937ar.c"])

setup(name="mersenne_random",
      ext_modules = cythonize([ext]))

Overwriting setup.py

! python setup.py build_ext -i &> /dev/null

import mt_random

mt_random.init_state(123)
for i in range(10):
    print mt_random.rand(),
print

0.696469187433 0.712955321584 0.28613933881 0.428470925062 0.226851454989 0.690884851546 0.55131476525 0.71915030892 0.719468970718 0.491118932723