How to use the plac.parser_from function in plac

def check_help(name):
    sys.argv[0] = name + '.py'  # avoid issue with pytest
    plac_core._parser_registry.clear()  # makes different imports independent
    try:
        try:
            main = plac.import_main(name + '.py')
        except SyntaxError:
            if sys.version < '3':  # expected for Python 2.X
                return
            else:  # not expected for Python 3.X
                raise
        p = plac.parser_from(main)
        expected = fix_today(open(name + '.help').read()).strip()
        got = p.format_help().strip()
        assert got == expected, got
    finally:
        sys.argv[0] = sys_argv0

def parser_from(f, **kw):
    f.__annotations__ = kw
    return plac.parser_from(f)

def main(verbose, interactive, multiline, serve, batch, test, fname=None,
         *extra):
    "Runner for plac tools, plac batch files and plac tests"
    baseparser = plac.parser_from(main)
    if fname is None:
        baseparser.print_help()
    elif sys.argv[1] == fname:  # script mode
        plactool = plac.import_main(fname)
        plactool.prog = os.path.basename(sys.argv[0]) + ' ' + fname
        out = plac.call(plactool, sys.argv[2:], eager=False)
        if plac.iterable(out):
            for output in out:
                print(output)
        else:
            print(out)
    elif interactive or multiline or serve:
        plactool = plac.import_main(fname, *extra)
        plactool.prog = ''
        i = plac.Interpreter(plactool)
        if interactive: