Bug report

Next code:

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

Adding __slots__ = () to A and B definitions fixes the error:

class A(int):
    __slots__ = ()

class B(int):
    __slots__ = ()

a = A(1)
a.__class__ = B

Is it an expected difference in behavior for int and float?

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.

Your environment

• CPython versions tested on: 3.10.8
• Operating system and architecture: Windows 10, 64bit