def sanity_check_args(args):
    """
    Check that command-line arguments are self-consistent.
    """
    if args.weeks_ahead and (args.gw_start or args.gw_end):
        raise RuntimeError("Please only specify weeks_ahead OR gw_start/end")
    elif (args.gw_start and not args.gw_end) or (args.gw_end and not args.gw_start):
        raise RuntimeError("Need to specify both gw_start and gw_end")
    if args.num_free_transfers and args.num_free_transfers not in range(1, 3):
        raise RuntimeError("Number of free transfers must be 1 or 2")
    return True