def maybe_download_and_extract():
    """Download and extract the tarball from Alex's website."""
    dest_directory = FLAGS.data_dir
    if not os.path.exists(dest_directory):
        os.makedirs(dest_directory)
    filename = DATA_URL.split('/')[-1]
    filepath = os.path.join(dest_directory, filename)
    if not os.path.exists(filepath):

        def _progress(count, block_size, total_size):
            sys.stdout.write('\r>> Downloading %s %.1f%%' %
                             (filename, float(count * block_size) /
                              float(total_size) * 100.0))
            sys.stdout.flush()

        filepath, _ = urllib.request.urlretrieve(DATA_URL, filepath, _progress)
        print()
        statinfo = os.stat(filepath)
        print('Successfully downloaded', filename, statinfo.st_size, 'bytes.')
        tarfile.open(filepath, 'r:gz').extractall(dest_directory)
Download and extract the tarball from Alex's website.
train_cifar.py