Add an unstable C API for immortalizing objects

[ngoldbaum]

I'd like to add a new C API to allow extensions to mark objects as immortal. See https://discuss.python.org/t/add-an-unstable-c-api-for-immortalizing-objects/105461 for discussion. I'm opening this issue to link a future PR and for visibility for people who don't look at discourse regularly.

Linked PRs

• gh-143300: implement PyUnstable_SetImmortal #144543

[picnixz]

Considering this idea was already supported by a core dev and that another core dev chimed in to support it, I think it's fine to keep the issue. However, please note that I would have closed it because we don't want issues just for visibility or PRs just for PoCs. Those should be kept in forks, and discussion should still be kept on DPO.

However, if the proposal becomes too large, it may require a PEP, in which case I'd prefer closing the issue now instead of having back and forth.

@ZeroIntensity Do you think this requires a PEP? if so, I'd rather close this issue now as the process may be long.

[ZeroIntensity]

This shouldn't need a PEP, as the idea and implementation are pretty simple. (This isn't proposing immortalization for arbitrary objects; that would require a PEP.) Though we should try to get the C API WG's blessing, because I suspect Petr has some reservations about the dangers of immortality.