code: def extra_reading_spec(self):
      
      field_names = ("frame_number", "action", "reward", "done")
      data_fields = {
          name: tf.FixedLenFeature([1], tf.int64) for name in field_names
      }
      decoders = {
          name: tf.contrib.slim.tfexample_decoder.Tensor(tensor_key=name)
          for name in field_names
      }
      return (data_fields, decoders)
docs: Additional data fields to store on disk and their decoders.