code: def __choose_persona_from_text(self, utt):
      utt = utt.strip()
      if utt not in self.utterance_to_persona_map:
          best_word_overlap = 0
          best_persona = None
          for p in self.personas:
              word_overlap = self.__calculate_word_overlap(utt, p)
              if word_overlap >= best_word_overlap:
                  best_word_overlap = word_overlap
                  best_persona = p
          if not best_persona:
              raise Exception(
                  f'No persona found for utterance: "{utt}". This should not happen.'
              )
          self.utterance_to_persona_map[utt] = best_persona
          # Should have a \n at the end of it already
          return best_persona
      return self.utterance_to_persona_map[utt]
  
imports: import copy
  import os
  import random
  import re
  from collections import defaultdict
  from typing import List, Optional, Dict, Tuple
  from parlai.core.opt import Opt
  from parlai.core.teachers import ParlAIDialogTeacher, create_task_agent_from_taskname
  from parlai.tasks.convai2.agents import BothTeacher
  from parlai.tasks.empathetic_dialogues.agents import EmpatheticDialoguesTeacher
  from parlai.tasks.wizard_of_wikipedia.agents import WizardDialogKnowledgeTeacher
  from parlai.utils.misc import warn_once
  from parlai.utils.io import PathManager
  from .build import build
label_desc: Use image node_id 4 for calling the PersonaTopicifier obj's underlying member method code with example usage: obj.__choose_persona_from_text(utt) and returns: self, best_persona