docs: def _batch_to_stdin(process, in_record_sep, in_column_sep, in_batches, batch_to_file_s):
          """Write in-batch contents to `process` 's stdin (if necessary)
          """
          for i, b2f in enumerate(batch_to_file_s):
              if b2f.is_stdin():
                  input_str = BaseShellOperator._input_str(in_batches[i], in_record_sep, in_column_sep)
                  b2f.write_stdin(process.stdin, input_str)
                  break