code: def _read_checkpoint_vars(model_path):
          
          reader = tf.train.NewCheckpointReader(model_path)
          reader = CheckpointReaderAdapter(reader)    # use an adapter to standardize the name
          ckpt_vars = reader.get_variable_to_shape_map().keys()
          return reader, set(ckpt_vars)
docs: return a set of strings