Python and C with ctypes

Calling C code from Python is very simple using ctypes. Here is a very simple example to get you started and to serve as a reminder for me!

Let's say you have this C file, defining 3 functions:

foo which prints something to stdout;
bar which returns and int;
baz which takes a parameter and returns a value.

	#include <stdio.h>

	void foo() {
	printf("Hello world\n");
	}

	int bar() {
	return 1;
	}

	int baz(int n) {
	int sum = 0;
	for (int i = 0; i < n; i++) {
	sum += i;
	}
	return sum;
	}

view raw go.c hosted with ❤ by GitHub

First, you want to compile this C file into a shared object. Here is a Makefile to do just this: simple type make all and you're done.

	all: go.so

	go.o: go.c
	gcc -std=c99 -c -fPIC go.c -o go.o

	go.so: go.o
	gcc -shared -Wl,-soname,libgo.so -o libgo.so go.o

view raw Makefile hosted with ❤ by GitHub

Finally, you can call these C functions from Python using ctypes:

	import ctypes

	libgo = ctypes.cdll.LoadLibrary('./libgo.so')
	libgo.foo()
	print(libgo.bar())
	print(libgo.baz(100))

view raw go.py hosted with ❤ by GitHub

Obviously, there is much more to it and things get more complicated soon, but, as you can see, for simple tasks like this using ctypes is pretty straitforward.