def iso8601interval(value, argument='argument'):

    try:
        start, end = _parse_interval(value)

        if end is None:
            end = _expand_datetime(start, value)

        start, end = _normalize_interval(start, end, value)

    except ValueError:
        msg = 'Invalid {arg}: {value}. {arg} must be a valid ISO8601 date/time interval.'
        raise ValueError(msg.format(arg=argument, value=value),)

    return start, end
check if there are untagged networks on the same interface
dataset/ETHPy150Open noirbizarre/flask-restplus/flask_restplus/inputs.py/iso8601interval--crossover with--dataset/ETHPy150Open openstack/fuel-web/nailgun/nailgun/extensions/network_manager/checker.py/NetworkCheck.check_untagged_intersection