https://blog.csdn.net/lyh66/article/details/50098739
https://blog.csdn.net/cashey1991/article/details/7942809
https://blog.csdn.net/coding__madman/article/details/51043733
https://www.jianshu.com/p/80cdbf718916
符号常量 数值 Meaning
no_argument 0 无参数
required_argument 1 有参数
optional_argument
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