code: def download(directory, filename):
    
    filepath = os.path.join(directory, filename)
    if tf.gfile.Exists(filepath):
      return filepath
    if not tf.gfile.Exists(directory):
      tf.gfile.MakeDirs(directory)
    url = 'http://yann.lecun.com/exdb/mnist/' + filename + '.gz'
    _, zipped_filepath = tempfile.mkstemp(suffix='.gz')
    print('Downloading %s to %s' % (url, zipped_filepath))
    urllib.request.urlretrieve(url, zipped_filepath)
    with gzip.open(zipped_filepath, 'rb') as f_in, \
        tf.gfile.Open(filepath, 'wb') as f_out:
      shutil.copyfileobj(f_in, f_out)
    os.remove(zipped_filepath)
    return filepath
docs: Download (and unzip) a file from the MNIST dataset if not already done.