def get_dir_from_zipfile(zip_file, fallback=None):
    """Return the name of the root folder in a zip file.

    :param zip_file: a :class:`zipfile.ZipFile` instance.
    :param fallback: if `None`, the name of the zip file is used. This is
        returned if the zip file contains more than one top-level directory,
        or none at all.
    """
    fallback = fallback or zip_file.filename
    directories = [name for name in zip_file.namelist() if name.endswith("/")
                   and len(PurePath(name).parts) == 1]
    return fallback if len(directories) > 1 else directories[0]
def _file_name_to_batch_number(example_file_name):
    """Parses batch number from file.

    :param example_file_name: See doc for `find_example_file`.
    :return: batch_number: Integer.
    :raises: ValueError: if batch number cannot be parsed from file name.
    """

    pathless_file_name = os.path.split(example_file_name)[-1]
    extensionless_file_name = os.path.splitext(pathless_file_name)[0]
    return int(extensionless_file_name.split('input_examples_batch')[-1])