class_docstr: End-to-end negotiation teacher that loads the data from
  https://github.com/facebookresearch/end-to-end-negotiator.
class_docstr_tok: ["End-to-end","negotiation","teacher","that","loads","the","data","from","https",":","\/\/github.com\/facebookresearch\/end-to-end-negotiator","."]
code: def _start_dialogue(self):
      words = self.episodes[self.episode_idx].strip().split()
      self.values = get_tag(words, INPUT_TAG)
      self.dialogue = self._split_dialogue(get_tag(words, DIALOGUE_TAG))
      self.output = get_tag(words, OUTPUT_TAG)
      # The dialogue should end with a selection token
      assert self.dialogue[-1][1] == SELECTION_TOKEN
  
      (
          book_cnt,
          book_val,
          hat_cnt,
          hat_val,
          ball_cnt,
          ball_val,
      ) = self.values
      welcome = WELCOME_MESSAGE.format(
          book_cnt=book_cnt,
          book_val=book_val,
          hat_cnt=hat_cnt,
          hat_val=hat_val,
          ball_cnt=ball_cnt,
          ball_val=ball_val,
      )
  
      self.dialogue_idx = -1
      if self.dialogue[0][0] == THEM_TOKEN:
          action = self._continue_dialogue()
          action["text"] = welcome + "\n" + action["text"]
      else:
          action = self._continue_dialogue(skip_teacher=True)
          action["text"] = welcome
  
      action["items"] = {
          "book_cnt": book_cnt,
          "book_val": book_val,
          "hat_cnt": hat_cnt,
          "hat_val": hat_val,
          "ball_cnt": ball_cnt,
          "ball_val": ball_val,
      }
  
      return action
  
imports: from parlai.core.teachers import Teacher
  from .build import build
  from parlai.utils.io import PathManager
  import os
  import random
label_desc: Use image node_id 10 for calling the NegotiationTeacher obj's underlying member method code with example usage: obj._start_dialogue() and returns: action