Int and float different behavior with TypeError "object layout differs from"

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1

Minimal repro to illustrate my question:

class A(int):
    pass

class B(int):
    pass

a = A(1)
a.__class__ = B

results in TypeError: __class__ assignment: 'B' object layout differs from 'A'

The very same code for float won’t throw any error:

class C(float):
    pass

class D(float):
    pass

c = C(1.2)
c.__class__ = D

I also found out that if I add __slots__ = () attribute to both A and B definitions no errors will appear in the __class__ reassignment.

Is this different behavior for int and float an expected one?

P.S. Real code is in the autoreload extension for jupyter, where it tries to reload the changed class and if it’s a child of int it throws this error.

Python version 3.10.8.