python memorize function for cache

memorize.py

import functools
import inspect
import time
import random


def memorize(keyfn, scenario='default', timeout=300):
    def wrapper(fn):
        _cached = {}

        functools.wraps(fn)
        def wrapped(*args, **kw):
            now = time.time()
            key = keyfn(fn, *args, **kw)

            if key in _cached:
                (expire_at, result) = _cached[key]
                if now < expire_at:
                    return result

            result = fn(*args, **kw)
            if scenario == 'default':
                expire_at =  now + timeout
            elif scenario == 'this-hour':
                expire_at =  now + (3600 - (now % 3600))
            else:
                raise Exception('unknow memorize scenario')
            _cached[key] = (expire_at, result)
            return result

        def purge_cache():
            """default is clear all."""
            for k in _cached.keys():
                del _cached[k]
            return

        wrapped._cached = _cached
        wrapped.purge_cache = purge_cache
        return wrapped

    return wrapper

@memorize(keyfn=lambda fn, *args, **kw: args[0], timeout=1)
def foo(n):
    return n + random.random()

print foo(2)
time.sleep(0.5)
print foo(2)
time.sleep(1)
print foo(2)
print foo(2)
foo.purge_cache()
print foo(2)
print foo(2)