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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 update_list(self, list_id, name=None, mode=None, description=None):
 """ Update a list :param list_id: list ID number :param name: New name for the list :param mode: :code:`'public'` (default) or :code:`'private'` :param description: New description of the list :return: The updated list object :rtype: :class:`~responsebot.models.List` """

        return List(tweepy_list_to_json(
            self._client.update_list(list_id=list_id, name=name, mode=mode, description=description))
        )