Python：__ add__和+，与float和integer不同的行为 [英] Python: __add__ and +, different behavior with float and integer

问题描述

将整数值添加到浮点值时，我意识到 __ add __ 方法可以在浮点数上正常运行，例如：

When adding an integer value to a float value, I realized that __add__ method is working fine if called on float, such as this:

>>> n = 2.0
>>> m = 1
>>> n.__add__(m)
3.0

，但如果对整数调用则不会：

but not if called on an integer:

>>> m.__add__(n)
NotImplemented

起初我以为 __ add __ 只是针对 int 和 float 类型（例如接受float类型）的实现方式有所不同被添加到int类型，但不是相反）。然后我注意到，如果我改用+运算符，则一切正常：

At first I thought that __add__ was just being implemented differently for int and float types (like float types accepting to be added to int types, but not the opposite). Then I noticed that everything works fine if I use the + operator instead:

>>> n + m
3.0
>>> m + n
3.0

有人知道为什么会这样吗？ __ add __ 和 + 彼此之间没有很深的联系吗？

Does anybody know why this is happening? Are __add__ and + not deeply related to each other?

推荐答案

a + b 不能直接转换为 a .__ add __（b）。如果 a .__ add __ 不存在或返回 b .__ radd __（a） > NotImplemented ，或者如果 b 是 a 类型的子类型的实例

a + b does not directly translate to a.__add__(b). It also tries b.__radd__(a) if a.__add__ doesn't exist or returns NotImplemented, or if b is an instance of a subtype of a's type.

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