在Python中分配实例的__class__属性 [英] Assigning to an instance's __class__ attribute in Python

问题描述

在什么情况下，什么时候不可能在Python中分配实例的__class__属性?

Under what circumstances is it possible, and when is it impossible, to assign to an instance's __class__ attribute in Python?

诸如TypeError: __class__ assignment: only for heap types之类的错误消息对我而言并不是真的.

Error messages such as TypeError: __class__ assignment: only for heap types don't really do it for me.

推荐答案

您只能分配给用户定义的类(即使用class关键字定义的)实例的__class__属性，值也必须是用户定义的类.这些类是新样式还是旧样式都没有关系. (但是，您不能将它们混合使用.您不能将旧式类实例转换为新式类实例.)另请参见 Python错误跟踪器中的="noreferrer">此问题，它还抱怨该错误消息有些难以理解.

You can only assign to the __class__ attribute of an instance of a user-defined class (i.e. defined using the class keyword), and the new value must also be a user-defined class. Whether the classes are new-style or old-style does not matter. (You can't mix them, though. You can't turn an old-style class instance into a new-style class instance.) See also this issue in the Python bug tracker, which also complains that the error message is somewhat hard to understand.

只需添加Rafe在上面的评论中所说的话:绝对不要在生产中这样做.

Just to add what Rafe said in the above comment: Never do this in production.

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