code: def save(df, path):
          
          if os.environ.get('TENSORPACK_COMPATIBLE_SERIALIZE', 'msgpack') == 'msgpack':
              def _dumps(dp):
                  return dumps(dp)
          else:
              def _dumps(dp):
                  return dumps(dp).to_pybytes()
  
          size = _reset_df_and_get_size(df)
          with tf.python_io.TFRecordWriter(path) as writer, get_tqdm(total=size) as pbar:
              for dp in df:
                  writer.write(_dumps(dp))
                  pbar.update()
docs: Args:
              df (DataFlow): the DataFlow to serialize.
              path (str): output tfrecord file.