__new__方法理解

class Foo(object):
    def __init__(self, *args, **kwargs):
        pass
    def __new__(cls, *args, **kwargs):
        return object.__new__(cls, *args, **kwargs)

# 以上return等同于
# return object.__new__(Foo, *args, **kwargs)

class Child(Foo):
    def __new__(cls, *args, **kwargs):
        return object.__new__(cls, *args, **kwargs)

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class Round2Float(float):
    def __new__(cls,num):
        num = round(num,2)
        obj = float.__new__(Round2Float,num)
        return obj

f=Round2Float(4.324599)
print(f)
'''派生不可变类型'''

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2020-05-08