class method __instancecheck__ does not work

Question

I am using python 2.7.3 on Windows. I tried to override the __instancecheck__ magic method as a class method. But I can not make it work.

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Answer 1

The docs say:

Note that these methods are looked up on the type (metaclass) of a class. They cannot be defined as class methods in the actual class. This is consistent with the lookup of special methods that are called on instances, only in this case the instance is itself a class.

http://docs.python.org/2/reference/datamodel.html#customizing-instance-and-subclass-checks