class_docstr: TaskNTalk basic teacher, it picks a random image and associates a random task with
  it.
  
  Metric updates and observation are to be implemented.
code: def __len__(self):
      return len(self.data)
  
imports: from parlai.core.teachers import Teacher
  from parlai.utils.io import PathManager
  from .build import build
  import json
  import os
  import random
label_desc: Use image node_id 4 for calling the AbstractTaskNTalk obj's underlying member method code with example usage: obj.__len__() and returns: len