Also I just noticed this statement:

> In current CPython, for your ForeverObject(False), `del o` does not make the object trash "for real".  __del__ runs immediately (due to deterministic, synchronous reference counting) and resurrects it.  That cuts off the "about to have its memory destroyed and recycled" part, so the callback doesn't run.

The problem is the callback _does_ run even though the object is resurrected! :)

(Only if going through gc)