code: def _set_up_sent_tok(self):
      try:
          import nltk
      except ImportError:
          raise ImportError(
              "Please install nltk (e.g. pip install nltk)."
          )
      # nltk-specific setup
      st_path = "tokenizers/punkt/{0}.pickle".format("english")
      try:
          self.sent_tok = nltk.data.load(st_path)
      except LookupError:
          nltk.download("punkt")
          self.sent_tok = nltk.data.load(st_path)
  
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 5 for calling the KnowledgeRetrieverAgent obj's underlying member method code with example usage: obj._set_up_sent_tok() without return types