code: def get_sentence_tokenizer():
      """
      Loads the nltk sentence tokenizer.
      """
      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:
          sent_tok = nltk.data.load(st_path)
      except LookupError:
          nltk.download("punkt")
          sent_tok = nltk.data.load(st_path)
      return sent_tok
  
imports: import copy
  import json
  import os
  from typing import Optional
  from parlai.core.params import ParlaiParser
  from parlai.core.message import Message
  from parlai.core.opt import Opt
  from parlai.core.teachers import FixedDialogTeacher, DialogTeacher, ParlAIDialogTeacher
  from parlai.tasks.wrapper.agents import AbstractWrapperTeacher
  from parlai.utils.io import PathManager
  from .build import build
label_desc: Use image node_id 1 for calling a global function with example usage: get_sentence_tokenizer() and returns: sent_tok