Behavior change for `foo and 1 or 2`: 3.12 newly converts `foo` to bool twice

Bug report

Bug description:

We noticed a behavior change between 3.11 and 3.12. The following code calls Foo.__bool__ once in 3.11 and twice in 3.12. Consequently for this contrived example, the expression evaluates to different results in 3.11 and 3.12.

class Foo:
    def __init__(self):
        self._a = True
    def __bool__(self):
        self._a = not self._a
        print(f"Foo.__bool__ -> {self._a}")
        return self._a

Foo() and "a string" or 42

In Python 3.11:

>>> Foo() and "a string" or 42
Foo.__bool__ -> False
42

In Python 3.12 (and 3.13.0b2):

>>> Foo() and "a string" or 42
Foo.__bool__ -> False
Foo.__bool__ -> True
<__main__.Foo object at 0x7f0ae554c1a0>

Is this change intentional?

Note that I'm not necessarily asking to change this. We should arguably change the code to "a string" if Foo() else 42, which evaluates the same in 3.11 and 3.12.

CPython versions tested on:

3.12

Operating systems tested on:

Linux

Linked PRs

• gh-124394
• gh-124723

Ejecuta el reproductor proporcionado de Foo.__bool__ en Python 3.11, 3.12 y 3.13; después, revisa los PR vinculados gh-124394 y gh-124723 para conocer la dirección actual. Se considera terminado cuando el cambio de comportamiento se haya resuelto o documentado explícitamente, cuente con cobertura de regresión y el resultado esperado esté claro.