code: def _xml_for_episode_index(self, ep_ind):
          
  
          # read the model xml, using the metadata stored in the attribute for this episode
          model_file = self.demo_file["data/{}".format(ep_ind)].attrs["model_file"]
          model_path = os.path.join(self.demo_path, "models", model_file)
          with open(model_path, "r") as model_f:
              model_xml = model_f.read()
          return model_xml
docs: Helper method to retrieve the corresponding model xml string
          for the passed episode index.