def get_user_tweets(self, auth_secret, username, max_cnt_tweets):
        """Get the tweets posted by one user.

        Parameters
        ----------
        auth_secret: str
            The authentication secret of the logged-in user.
        username:
            The name of the user who post the tweets and may not be the logged-in user.
        max_cnt_tweets: int
            The maximum number of tweets included in the return. If it is set to -1,
            then all the tweets posted by the user will be included.

        Returns
        -------
        bool
            True if the tweets are successfully retrieved, False otherwise.
        result
            A dict containing a list of tweets with the key TWEETS_KEY if
            the tweets are successfully retrieved, a dict containing
            the error string with the key ERROR_KEY otherwise.

        Note
        ----
        Possible error strings are listed as below:

        -  ERROR_NOT_LOGGED_IN
        -  ERROR_USERNAME_NOT_EXIST_FORMAT.format(username)
        """
        result = {pytwis_constants.ERROR_KEY: None}

        # Check if the user is logged in.
        loggedin, _ = self._is_loggedin(auth_secret)
        if not loggedin:
            result[pytwis_constants.ERROR_KEY] = pytwis_constants.ERROR_NOT_LOGGED_IN
            return (False, result)

        # Get the userid from the username.
        userid = self._rc.hget(pytwis_constants.USERS_KEY, username)
        if userid is None:
            result[pytwis_constants.ERROR_KEY] = \
                pytwis_constants.ERROR_USERNAME_NOT_EXIST_FORMAT.format(username)
            return (False, result)

        # Get the tweets posted by the user.
        user_tweets_key = pytwis_constants.USER_TWEETS_KEY_FORMAT.format(userid)

        result[pytwis_constants.TWEETS_KEY] = \
            self._get_tweets(user_tweets_key, max_cnt_tweets)
        return (True, result)
Get the tweets posted by one user.

        Parameters
        ----------
        auth_secret: str
            The authentication secret of the logged-in user.
        username:
            The name of the user who post the tweets and may not be the logged-in user.
        max_cnt_tweets: int
            The maximum number of tweets included in the return. If it is set to -1,
            then all the tweets posted by the user will be included.

        Returns
        -------
        bool
            True if the tweets are successfully retrieved, False otherwise.
        result
            A dict containing a list of tweets with the key TWEETS_KEY if
            the tweets are successfully retrieved, a dict containing
            the error string with the key ERROR_KEY otherwise.

        Note
        ----
        Possible error strings are listed as below:

        -  ERROR_NOT_LOGGED_IN
        -  ERROR_USERNAME_NOT_EXIST_FORMAT.format(username)