docs: def _get_tweets(self, tweets_key, max_cnt_tweets):
          """Get at most `max_cnt_tweets` tweets from the Redis list `tweets_key`.
  
          Parameters
          ----------
          tweets_key: str
              The key of the Redis list which stores the tweets.
          max_cnt_tweets: int
              The maximum number of tweets included in the returned list. If it is set to -1,
              then all the available tweets will be included.
  
          Returns
          -------
          tweets
              A list of tweets
          """
          tweets = []
          if max_cnt_tweets == 0:
              return tweets
          elif max_cnt_tweets == -1:
              # Return all the tweets in the timeline.
              last_tweet_index = -1
          else:
              # Return at most max_cnt_tweets tweets.
              last_tweet_index = max_cnt_tweets - 1
  
          # Get the post IDs of the tweets.
          post_ids = self._rc.lrange(tweets_key, 0, last_tweet_index)
  
          if not post_ids:
              return tweets
  
          with self._rc.pipeline() as pipe:
              # Get the tweets with their user IDs and UNIX timestamps.
              pipe.multi()
              for post_id in post_ids:
                  post_id_key = pytwis_constants.TWEET_KEY_FORMAT.format(post_id)
                  pipe.hgetall(post_id_key)
              tweets = pipe.execute()
  
              # Get the userid-to-username mappings for all the user IDs associated with the tweets.
              userid_set = {tweet[pytwis_constants.TWEET_USERID_KEY] for tweet in tweets}
              userid_list = []
              pipe.multi()
              for userid in userid_set:
                  userid_list.append(userid)
                  userid_key = pytwis_constants.USER_PROFILE_KEY_FORMAT.format(userid)
                  pipe.hget(userid_key, pytwis_constants.USERNAME_KEY)
              username_list = pipe.execute()
  
          userid_to_username = {userid: username for userid, username in\
                                zip(userid_list, username_list)}
  
          # Add the username for the user ID of each tweet.
          for tweet in tweets:
              tweet[pytwis_constants.USERNAME_KEY] = \
                  userid_to_username[tweet[pytwis_constants.TWEET_USERID_KEY]]
  
          return tweets