python3高级语法:__slots__属性、property装饰器、上下文管理协议、__new__方法
#practice29:派生内置不可变类型并修改其实例化行为(以tuple为例)__new__()isintendedmainlytoallowsubclassesofimmutabletypes(likeint,str,ortuple)tocustomizeinstancecreation.__init__()Calledaftertheinstancehasbeencreated(by__ne