Python decorator to memoize functions.

memoize.py

import unittest


# a generic function decorator to memoize call results
class Memoize(object):

    def __init__(self, func):
        self.func = func
        self._cache = {}
        self._count = 0

    @property
    def count(self):
        return self._count

    def __call__(self, *args):
        try:
            return self._cache[args]
        except KeyError:
            value = self.func(*args)
            self._cache[args] = value
            self._count += 1
            return value


@Memoize
def factorial(num):
    if num in (0, 1):
        return 1
    return num * factorial(num - 1)


@Memoize
def fibonacci(num):
    if num in (0, 1):
        return num
    return fibonacci(num - 1) + fibonacci(num - 2)


class MemoizeTest(unittest.TestCase):

    def test_factorial(self):
        self.assertEquals(120, factorial(5))
        self.assertEquals(5, factorial.count)

    def test_fibonacci(self):
        self.assertEquals(144, fibonacci(12))
        self.assertEquals(13, fibonacci.count)  # without memoization: 465 calls would've been made!


if __name__ == '__main__':
    unittest.main()