[3.14] change in behaviour in gc.get_referrers(some_local)

[graingert]

Bug report

Bug description:

import gc

async def demo():
    class A:
        pass

    a = A()
    print(gc.get_referrers(a))

try:
    demo().send(None)
except StopIteration as e:
    print(f"{e.value=}")

on 3.11-3.13 this prints:

[]
e.value=None

on 3.14 this prints:

[<coroutine object demo at 0x7d00fff85000>]
e.value=None

this makes gc.get_referrers less useful in detecting cyclic garbage where I'd like to be able to make the assertion that the current frame is the only referrer to an Exception.

the alternative is to hold a weak reference to the object, delete the object and see if the weak reference is dead with the gc disabled. But then I don't get any debug information in my failing test of why the object is still alive.

CPython versions tested on:

3.14, CPython main branch

Operating systems tested on:

Linux

note: @markshannon asked me to open this issue

Linked PRs

• gh-125640

[graingert]

The behavior change was caused by this PR https://github.com/python/cpython/pull/124392