Python data descriptor did not work as instance variable? [duplicate]

Answer 1

The descriptor how-to is wrong here. The Python data model has the correct description:

The following methods [__get__, __set__, and __delete__] only apply when an instance of the class containing the method (a so-called descriptor class) appears in an owner class (the descriptor must be in either the owner’s class dictionary or in the class dictionary for one of its parents).

Descriptors have to be class attributes.