code: def _subset_filenames(dl_paths, split):
    
    assert isinstance(dl_paths, dict), dl_paths
    # Get filenames for a split.
    if split == tfds.Split.TRAIN:
      urls = _get_url_hashes(dl_paths['train_urls'])
    elif split == tfds.Split.VALIDATION:
      urls = _get_url_hashes(dl_paths['val_urls'])
    elif split == tfds.Split.TEST:
      urls = _get_url_hashes(dl_paths['test_urls'])
    else:
      logging.fatal('Unsupported split: %s', split)
    cnn = _find_files(dl_paths, 'cnn', urls)
    dm = _find_files(dl_paths, 'dm', urls)
    return cnn + dm
docs: Get filenames for a particular split.