<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def userstream_user(self, delegate, stall_warnings=None, with_='followings', replies=None):
 """ Streams messages for a single user. https://dev.twitter.com/docs/api/1.1/get/user The ``stringify_friend_ids`` parameter is always set to ``'true'`` for consistency with the use of string identifiers elsewhere. :param delegate: A delegate function that will be called for each message in the stream and will be passed the message dict as the only parameter. The message dicts passed to this function may represent any message type and the delegate is responsible for any dispatch that may be required. (:mod:`txtwitter.messagetools` may be helpful here.) :param bool stall_warnings: Specifies whether stall warnings should be delivered. :param str with_: If ``'followings'`` (the default), the stream will include messages from both the authenticated user and the authenticated user's followers. If ``'user'``, the stream will only include messages from (or mentioning) the autheticated user. All other values are invalid. (The underscore appended to the parameter name is to avoid conflicting with Python's ``with`` keyword.) :param str replies: If set to ``'all'``, replies to tweets will be included even if the authenticated user does not follow both parties. :returns: An unstarted :class:`TwitterStreamService`. """

        params = {'stringify_friend_ids': 'true'}
        set_bool_param(params, 'stall_warnings', stall_warnings)
        set_str_param(params, 'with', with_)
        set_str_param(params, 'replies', replies)

        svc = TwitterStreamService(
            lambda: self._get_userstream('user.json', params),
            delegate)
        return svc