def _add_baseline_to_exclude_files(args):
    """
    Modifies args.exclude_files in-place.
    """
    baseline_name_regex = '^{}$'.format(args.import_filename[0])
    if not args.exclude_files:
        args.exclude_files = baseline_name_regex
    elif baseline_name_regex not in args.exclude_files:
        args.exclude_files += '|{}'.format(baseline_name_regex)
