parse_args() 方法提供了一个 default 参数用于设置默认值。如：
- parser.add_option(“-f”,“–file”, action=“store”, dest=“filename”, default=“foo.txt”)
- parser.add_option(“-v”, action=“store_true”, dest=“verbose”, default=True)
https://www.lmlphp.com/user/16709/article/item/583213/
http://www.cppcns.com/jiaoben/python/458775.html
