class_docstr: Abstract class for dialog problems.
code: def vocab_file(self):
      return self.vocab_filename
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import os
  import re
  import tarfile
  import zipfile
  import requests
  from tensor2tensor.data_generators import generator_utils
  from tensor2tensor.data_generators import problem
  from tensor2tensor.data_generators import text_encoder
  from tensor2tensor.data_generators import text_problems
  from tensor2tensor.data_generators.text_problems import VocabType
  from tensor2tensor.layers import modalities
  from tensor2tensor.utils import metrics
  import tensorflow.compat.v1
label_desc: Use image node_id 3 for calling the DialogAbstract obj's underlying member method code with example usage: obj.vocab_file() and returns: self