Demonstrates the problem with matplotlib resetting the random seed.

setup.py

#!/usr/bin/env python

from distutils.core import setup, Extension

modules = [
	Extension('_test',
		language='c++',
		sources=[
			'test.cpp'])]

setup(
	name='test',
	version='0.0.1',
	author='Lucas Theis',
	author_email='lucas@theis.io',
	ext_modules=modules)

test.cpp

#include <Python.h>
#include <stdlib.h>

#include <iostream>
using std::cout;
using std::endl;

PyObject* test(PyObject*, PyObject*, PyObject*) {
	cout << rand() % 100 << endl;
	cout << rand() % 100 << endl;
	cout << rand() % 100 << endl;
	cout << endl;

	Py_INCREF(Py_None);
	return Py_None;
}

static PyMethodDef test_methods[] = {
	{"test", (PyCFunction)test, METH_NOARGS, 0},
	{0}
};

PyMODINIT_FUNC init_test() {
	Py_InitModule3("_test", test_methods, 0);
}

test.py

from numpy.random import randn
from matplotlib.pyplot import imsave
from _test import test

I = randn(128, 128)

imsave('test.png', I)
test()

imsave('test.png', I)
test()