help — 指定帮助文档

parser.add_option("-f", "--filename",
                  metavar="FILE",
                  help="write output to FILE"),

optparse解析到 -h 或者 —help 命令行参数时，调用 parser.print_help()输出 程序帮助信息。help字段很有用。
metavar — 提示用户期望参数

Group — 给参数分组

group = OptionGroup(parser, ``Dangerous Options",
                    ``Caution: use these options at your own risk."
                    ``It is believed that some of them bite.")
group.add_option(``-g", action="store_true", help="Group option.")
parser.add_option_group(group)