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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def clean_cache(self):
 """ Clean cache with entries older than now because not used in future ;) :return: None """

        now = int(time.time())
        t_to_del = []
        for timestamp in self.cache:
            if timestamp < now:
                t_to_del.append(timestamp)
        for timestamp in t_to_del:
            del self.cache[timestamp]

        # same for the invalid cache
        t_to_del = []
        for timestamp in self.invalid_cache:
            if timestamp < now:
                t_to_del.append(timestamp)
        for timestamp in t_to_del:
            del self.invalid_cache[timestamp]