Thanks for the explanation! I agree that "about to be finalized" is unclear in the docs :)

I still believe that having different behavior for the ordering of finalizers versus weakref callbacks depending on whether the path is through gc versus reference counting is a bug.

The callback should be able to assume that when it's running, the referent is actually dead. The execution of a weakref callback in our case results in items being dropped from a WeakValueDictionary prematurely (the object is still referenced, accessible, and alive at the time the weakref callback runs).

I've attached a patch that would cause weakref callbacks to run consistently after finalizers. With the patch applied, all tests in cpython appear to pass, but the code examples above now work consistently.