Benjamin Peterson <benjamin@python.org> added the comment: This is not really accurate:

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class x(int): pass ... class y(object): pass ... x().__class__ = y Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: __class__ assignment: 'x' object layout differs from 'y' y().__class__ = x Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: __class__ assignment: 'y' object layout differs from 'x'

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