code: def fill_subparser(subparser):
      
      subparser.add_argument(
          "--dtype", help="dtype to save to; by default, images will be " +
          "returned in their original unsigned byte format",
          choices=('float32', 'float64', 'bool'), type=str, default=None)
      return convert_mnist
docs: Sets up a subparser to convert the MNIST dataset files.
  
      Parameters
      ----------
      subparser : :class:`argparse.ArgumentParser`
          Subparser handling the `mnist` command.