What's the public API alternative to _PyObject_GC_IS_TRACKED()?

[Dieter Maurer]

Marco Sulla wrote at 2021-12-29 11:59 +0100:
>On Wed, 29 Dec 2021 at 09:12, Dieter Maurer <dieter at handshake.de> wrote:
>> `MutableMapping` is a so called abstract base class (--> `abc`).
>>
>> It uses the `__subclass_check__` (and `__instance_check__`) of
>> `abc.ABCMeta` to ensure `issubclass(dict, MutableMapping)`.
>> Those can be customized by overriding `MutableMapping.__subclasshook__`
>> to ensure that your `frozendict` class (and their subclasses)
>> are not considered subclasses of `MutableMapping`.
>
>It does not work:
> ...
>>>> issubclass(fd, Mm)
>True

There is a cache involved. The `issubclass` above,
brings your `fd` in the `Mn`'s subclass cache.

> ...
>>>> Mm.__subclasshook__ = _my_subclasshook
>>>> issubclass(fd, Mm)
>True

See above.