compute_once.py

import functools

def compute_once(f):
    class ComputeOnce(object):
        def __call__(self):
            value = f()
            self.__class__.__call__ = lambda x: value
            return value
    return ComputeOnce()

def memoize(f):
    d = {}
    @functools.wraps(f)
    def compute(*args, **kwargs):
        key = (args, tuple(kwargs.items()))
        try:
            return d[key]
        except KeyError:
            value = f(*args, **kwargs)
            d[key] = value
            return value
    return compute

@memoize
def fib(n, a=1):
    print "fib(%d)" % n
    if n < 3:
        return 1
    else:
        return fib(n-1) + fib(n-2)

@compute_once
def return_one():
    print "Executing"
    return 1

@compute_once
def return_two():
    print "Executing"
    return 2

print fib
print fib(10, a=2)

print return_one
print return_one()
print return_one()
print return_two()
print return_two()