memorizing

# http://codereview.stackexchange.com/questions/137898/memoization-with-factorial-in-python
import functools

def memoize(func):
    cache = func.cache = {}

    @functools.wraps(func)
    def wrapper(n):
        if n not in cache:
            cache[n] = func(n)
        return cache[n]
    return wrapper

def memodict(f):
    """ Memoization decorator for a function taking a single argument """
    class memodict(dict):
        def __missing__(self, key):
            ret = self[key] = f(key)
            return ret
    return memodict().__getitem__

@memodict
# @memoize
def factorial(n):
    """calculates n! with a simple recursive algorithm"""
    if n == 0:
        return 1
    else:
        return n * factorial(n-1)