gistfile1.py

def cached(f):
    def wrapper(*args):
        if args not in wrapper.cache:
            wrapper.cache[args] = f(*args)
        return wrapper.cache[args]
    wrapper.cache = {}
    return wrapper

def factorial(n):
    print "Running factorial"
    result = 1
    for i in range(2, n + 1):
        result = result * i
    return result

factorial = cached(factorial)