code: def _set_up_tfidf_retriever(self, opt):
      retriever_opt = {
          "model_file": opt["retriever_model_file"],
          "remove_title": False,
          "datapath": opt["datapath"],
          "override": {"remove_title": False},
      }
      self.retriever = create_agent(retriever_opt)
  
      self._set_up_sent_tok()
      wiki_map_path = os.path.join(
          self.model_path, "chosen_topic_to_passage.json"
      )
      self.wiki_map = json.load(open(wiki_map_path, "r"))
  
imports: from typing import Optional
  from parlai.core.params import ParlaiParser
  from parlai.core.opt import Opt
  from parlai.core.agents import Agent, create_agent, create_agent_from_shared
  from parlai.core.torch_ranker_agent import TorchRankerAgent
  from parlai.tasks.wizard_of_wikipedia.agents import TOKEN_KNOWLEDGE
  from parlai.zoo.wizard_of_wikipedia.knowledge_retriever import download
  import json
  import os
label_desc: Use image node_id 3 for calling the KnowledgeRetrieverAgent obj's underlying member method code with example usage: obj._set_up_tfidf_retriever(opt) without return types