1.import as , 导入模块并另命名,便于记忆。import collections as _collections
2.ArgumentParser -- The main entry point for command-line parsing.
the add_argument() method is used to populate
the parser with actions for optional and positional arguments. Then
the parse_args() method is invoked to convert the args at the
command-line into an object with attributes.
ArgumentParser,命令行解析的主要接口。add_argument()方法用于通过添加位置参数和可选参数将行为构置于parser对象中,然后parse_args()方法
被激活,将命令行的参数变成带有属性的对象。