code: def fill_subparser(subparser):
      
      urls = ([None] * len(ALL_FILES))
      filenames = list(ALL_FILES)
      subparser.set_defaults(urls=urls, filenames=filenames)
      subparser.add_argument('-P', '--url-prefix', type=str, default=None,
                             help="URL prefix to prepend to the filenames of "
                                  "non-public files, in order to download them. "
                                  "Be sure to include the trailing slash.")
      return default_downloader
docs: Sets up a subparser to download the ILSVRC2012 dataset files.
  
      Note that you will need to use `--url-prefix` to download the
      non-public files (namely, the TARs of images). This is a single
      prefix that is common to all distributed files, which you can
      obtain by registering at the ImageNet website [DOWNLOAD].
  
      Note that these files are quite large and you may be better off
      simply downloading them separately and running ``fuel-convert``.
  
      .. [DOWNLOAD] http://www.image-net.org/download-images
  
  
      Parameters
      ----------
      subparser : :class:`argparse.ArgumentParser`
          Subparser handling the `ilsvrc2012` command.