A cache dict implementation with object level timeout

cache.py

import time
import collections


class Cache(collections.MutableMapping):

    def __init__(self, timeout=1, *args, **kwargs):
        self.__store = dict()
        self.__time_table = dict()
        self.__time_out = timeout
        # use the free update to set keys
        self.update(dict(*args, **kwargs))

    def __getitem__(self, key):
        if time.time() >= self.__time_table.get(key):
            del self.__store[key]
            del self.__time_table[key]
        return self.__store[key]

    def __setitem__(self, key, value):
        self.__store[key] = value
        self.__time_table[key] = time.time() + self.__time_out

    def __delitem__(self, key):
        del self.__store[key]
        del self.__time_table[key]

    def __contains__(self, item):
        if self.__time_table.get(item, None) is None:
            return False
        if time.time() >= self.__time_table.get(item):
            del self.__store[item]
            del self.__time_table[item]
            return False
        return True

    def __iter__(self):
        for item in iter(self.__store):
            if time.time() < self.__time_table.get(item):
                yield item

    def __len__(self):
        for item in iter(self.__store):
            if time.time() >= self.__time_table.get(item):
                del self.__store[item]
                del self.__time_table[item]
        return len(self.__store)


'''
cache = Cache(3)
cache["k1"] = "data1"
cache["k2"] = "data2"
time.sleep(1)
cache["k3"] = "data3"
time.sleep(1)
cache["k4"] = "data4"
while True:
    for item in iter(cache):
        print(item, cache[item])
    time.sleep(1)
'''