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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 add(self, entities):
 """ Adds the given entities to the cache, if they weren't saved before. """

        if not utils.is_list_like(entities):
            # Invariant: all "chats" and "users" are always iterables,
            # and "user" never is (so we wrap it inside a list).
            entities = itertools.chain(
                getattr(entities, 'chats', []),
                getattr(entities, 'users', []),
                (hasattr(entities, 'user') and [entities.user]) or []
            )

        for entity in entities:
            try:
                pid = utils.get_peer_id(entity)
                if pid not in self.__dict__:
                    # Note: `get_input_peer` already checks for `access_hash`
                    self.__dict__[pid] = utils.get_input_peer(entity)
            except TypeError:
                pass