class_docstr: VQA v2.0 Open-Ended teacher, which loads the json VQA data and implements the
  ``get`` method to return additional metadata.
code: def num_episodes(self):
      return self.num_examples()
  
imports: from parlai.utils.io import PathManager
  from parlai.core.teachers import FixedDialogTeacher
  from parlai.core.image_featurizers import ImageLoader
  from .build import build
  from parlai.tasks.coco_caption.build_2014 import buildImage
  from parlai.tasks.coco_caption.build_2015 import buildImage
  import json
  import os
label_desc: Use image node_id 4 for calling the OeTeacher obj's underlying member method code with example usage: obj.num_episodes() and returns: self