code: def num_examples(self):
      return self.num_exs
  
imports: import os
  import json
  from parlai.core.message import Message
  from parlai.core.teachers import FixedDialogTeacher
  from parlai.utils.io import PathManager
  from .build import build
label_desc: Use image node_id 3 for calling the Convai2Teacher obj's underlying member method code with example usage: obj.num_examples() and returns: self