Downloads and prepairs the dataset to be parsed by the data_generator.

def _download_and_parse_dataset(tmp_dir, train):
  """Downloads and prepairs the dataset to be parsed by the data_generator."""
  file_path = generator_utils.maybe_download(tmp_dir, _SNLI_ZIP, _SNLI_URL)
  zip_ref = zipfile.ZipFile(file_path, 'r')
  zip_ref.extractall(tmp_dir)
  zip_ref.close()

  file_name = 'train' if train else 'dev'
  dataset_file_path = os.path.join(tmp_dir, _SNLI_DATA_PATH % file_name)
  _parse_dataset(dataset_file_path, tmp_dir, train)