def _enforce_ttl_key(self, key):
        '''
        Enforce the TTL to a specific key, delete if its past TTL
        '''
        if key not in self._key_cache_time or self._ttl == 0:
            return
        if time.time() - self._key_cache_time[key] > self._ttl:
            del self._key_cache_time[key]
            dict.__delitem__(self, key)