__new__方法首先调用并返回一个实例化对象

1 >>> class CapStr(str):
2     def __new__(cls,string):
3         string = string.upper()
4         return str.__new__(cls,string)
5 
6     
7 >>> a = CapStr('afsgdfqwehu7348')
8 >>> a
9 'AFSGDFQWEHU7348'

 __new__方法首先调用并返回一个实例化对象