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

[Marco Sulla]

On Wed, 29 Dec 2021 at 00:03, Dieter Maurer <dieter at handshake.de> wrote:
> Why do you not derive from `dict` and override its mutating methods
> (to raise a type error after initialization is complete)?

I've done this for the pure py version, for speed. But in this way,
frozendict results to be a subclass of MutableMapping.