docs: def cache_clean(self):
  		"""
  		Remove expired items from the cache.
  		"""
  		now = time.time()
  		keys_for_removal = collections.deque()
  		for key, (_, expiration) in self.__cache.items():
  			if expiration < now:
  				keys_for_removal.append(key)
  		for key in keys_for_removal:
  			del self.__cache[key]