code: def print_topic(self, topicno, topn=10):
      """Get a single topic as a formatted string.
  
      Parameters
      ----------
      topicno : int
          Topic id.
      topn : int
          Number of words from topic that will be used.
  
      Returns
      -------
      str
          String representation of topic, like '-0.340 * "category" + 0.298 * "$M$" + 0.183 * "algebra" + ... '.
  
      """
      return " + ".join(
          '%.3f*"%s"' % (v, k)
          for k, v in self.show_topic(topicno, topn)
      )
  
label_desc: Use image node_id 1 for calling the BaseTopicModel obj's underlying member method code with example usage: obj.print_topic(topicno, topn) and returns: str