class_docstr: Index teacher where the labels are the sentences the contain the true answer.
code: def __init__(self, opt, shared=None):
      super().__init__(opt, shared)
  
      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.teachers import FixedDialogTeacher, DialogTeacher
  from parlai.utils.io import PathManager
  from .build import build
  import json
  import os
label_desc: Use image node_id 1 to create a new SentenceIndexTeacher object from inherited base classes: IndexTeacher with example: obj = SentenceIndexTeacher(opt, shared)