code: def get_filenames(is_training, data_dir):
    
    if is_training:
      return [
          os.path.join(data_dir, 'train-%05d-of-01024' % i)
          for i in range(_NUM_TRAIN_FILES)]
    else:
      return [
          os.path.join(data_dir, 'validation-%05d-of-00128' % i)
          for i in range(128)]
docs: Return filenames for dataset.