A cache decorator class with time-to-live support.

cache_with_ttl.py

import functools
import time


def hash_object(obj):
    if isinstance(obj, (tuple, list)):
        return (type(obj), tuple([hash_object(it) for it in obj]))
    elif isinstance(obj, dict):
        return (type(obj), tuple([(k, hash_object(v))
                                  for (k, v) in obj.iteritems()]))
    else:
        return obj


# https://wiki.python.org/moin/PythonDecoratorLibrary#Cached_Properties
class Cached(object):
    def __init__(self, ttl=300):
        self.ttl = ttl
        self._cache = {}

    def __call__(self, fn, *args, **kwargs):
        @functools.wraps(fn)
        def decorated(*args, **kwargs):
            # TODO: a better hash function?
            key = hash_object((args, kwargs))
            now = time.time()
            try:
                value, last_update = self._cache[key]
                if self.ttl > 0 and now - last_update > self.ttl:
                    raise AttributeError

            except (KeyError, AttributeError):
                value = fn(*args, **kwargs)
                self._cache[key] = (value, now)

            return value

        return decorated