python - __reduce__ 和 __reduce_ex__ 有什么区别？

Question

我知道这些方法是用于 pickle/解酸的，与 reduce 内置函数无关，但 2 有什么区别，为什么我们都需要？

Answer 1

The docs这么说

If provided, at pickling time__reduce__() will be called with noarguments, and it must return either astring or a tuple.

另一方面，

It is sometimes useful to know theprotocol version when implementing__reduce__. This can be done byimplementing a method named__reduce_ex__ instead of__reduce__. __reduce_ex__, when itexists, is called in preference over__reduce__ (you may still provide__reduce__ for backwardscompatibility). The __reduce_ex__method will be called with a singleinteger argument, the protocolversion.

在紧握的手上，Guido says这是一个可以清理的区域。