How to use the pkgconfig.default_prefix function in pkgconfig

opts.add_argument('--static', dest = 'static', action = 'store_true',
                      default = False,
                      help = 'Output libraries suitable for static linking')
    opts.add_argument('--dump', dest = 'dump', action = 'store_true',
                      default = False,
                      help = 'Dump the package if one is found.')

    args = opts.parse_args(argv[1:])

    if (args.exists and (args.exact_version or args.max_version)) or \
            (args.exact_version and (args.exists or args.max_version)) or \
            (args.max_version and (args.exists or args.exact_version)):
        raise error('only one of --exists, --exact-version, or --max-version')

    if args.dont_define_prefix:
        args.prefix = pkgconfig.default_prefix(False)

    exists = False

    ec = 1

    if args.atleast_pkgconfig_version:
        ec = 0
    else:
        ec, pkg, flags = pkgconfig.check_package(args.libraries, args, log, src)
        if ec == 0:
            if args.cflags:
                if len(flags['cflags']):
                    print(flags['cflags'])
                    log('cflags: %s' % (flags['cflags']))
                else:
                    log('cflags: empty')

action = version_action, nargs = 1, default = None,
                      help = 'The package is at least this version.')
    opts.add_argument('--exact-version', dest = 'exact_version', action = version_action,
                       nargs = 1, default = None,
                        help = 'The package is the exact version.')
    opts.add_argument('--max-version', dest = 'max_version', action = version_action,
                      nargs = 1, default = None,
                      help = 'The package is no later than this version.')
    opts.add_argument('--msvc-syntax', dest = 'msvc_syntax', action = 'store_true',
                      default = False,
                      help = 'Ignored')
    opts.add_argument('--dont-define-prefix', dest = 'dont_define_prefix', action = 'store_true',
                      default = False,
                      help = 'Ignored')
    opts.add_argument('--prefix-variable', dest = 'prefix', action = 'store',
                      nargs = 1, default = pkgconfig.default_prefix(),
                      help = 'Define the prefix.')
    opts.add_argument('--static', dest = 'static', action = 'store_true',
                      default = False,
                      help = 'Output libraries suitable for static linking')
    opts.add_argument('--dump', dest = 'dump', action = 'store_true',
                      default = False,
                      help = 'Dump the package if one is found.')

    args = opts.parse_args(argv[1:])

    if (args.exists and (args.exact_version or args.max_version)) or \
            (args.exact_version and (args.exists or args.max_version)) or \
            (args.max_version and (args.exists or args.exact_version)):
        raise error('only one of --exists, --exact-version, or --max-version')

    if args.dont_define_prefix: