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 _check_version(version, filename):
    major, minor = version.split('.')

    try:
        major = int(major)
    except ValueError as e:
        raise TransactionReplayError(
            filename,
            _('Invalid major version "{major}", number expected.').format(major=major)
        )

    try:
        int(minor)  # minor is unused, just check it's a number
    except ValueError as e:
        raise TransactionReplayError(
            filename,
            _('Invalid minor version "{minor}", number expected.').format(minor=minor)
        )

    if major != VERSION_MAJOR:
        raise IncompatibleTransactionVersionError(
            filename,
            _('Incompatible major version "{major}", supported major version is "{major_supp}".')
                .format(major=major, major_supp=VERSION_MAJOR)
        )