def snapshot_name(topo_name):
    """
    Get the snapshot name

    :param str topo_name: topology file location. The name is taken from the
                          directory containing the topology file using the
                          following format: topology_NAME_snapshot_DATE_TIME
    :return: snapshot name
    :raises ConvertError: when unable to determine the snapshot name
    """
    topo_name = os.path.basename(topology_dirname(topo_name))
    snap_re = re.compile('^topology_(.+)(_snapshot_)(\d{6}_\d{6})$')
    result = snap_re.search(topo_name)

    if result is not None:
        snap_name = result.group(1) + '_' + result.group(3)
    else:
        raise ConvertError('Unable to get snapshot name')

    return snap_name