Cython

CPython: a C implementation of Python. (others include PyPy)

Cython: C-extension of Python, allows to compile python code for speeding up.

The extension of Cython file is .pyx

Example

primes.pyx:

def primes(int nb_primes):
    cdef int n, i, len_p
    cdef int p[1000]
    if nb_primes > 1000:
        nb_primes = 1000

    len_p = 0  # The current number of elements in p.
    n = 2
    while len_p < nb_primes:
        # Is n prime?
        for i in p[:len_p]:
            if n % i == 0:
                break

        # If no break occurred in the loop, we have a prime.
        else:
            p[len_p] = n
            len_p += 1
        n += 1

    # Let's return the result in a python list:
    result_as_list  = [prime for prime in p[:len_p]]
    return result_as_list

to compile it:

setup.py

from setuptools import setup
from Cython.Build import cythonize

setup(
    ext_modules=cythonize("primes.pyx"),
)

python setup.py build_ext --inplace

to use it, in another python file:

import primes
primes.primes(10)

C library

from libc.stdlib cimport atoi

cdef parse_charptr_to_py_int(char* s):
    assert s is not NULL, "byte string value is NULL"
    return atoi(s)  # note: atoi() has no error detection!


from libc.math cimport sin

cdef double f(double x):
    return sin(x * x)

C++ library

# distutils: language=c++

from libcpp.vector cimport vector

def primes(unsigned int nb_primes):
    cdef int n, i
    cdef vector[int] p
    p.reserve(nb_primes)  # allocate memory for 'nb_primes' elements.

    n = 2
    while p.size() < nb_primes:  # size() for vectors is similar to len()
        for i in p:
            if n % i == 0:
                break
        else:
            p.push_back(n)  # push_back is similar to append()
        n += 1

    # Vectors are automatically converted to Python
    # lists when converted to Python objects.
    return p