import weakref
import trio
import gc

async def f():
    async with trio.open_nursery() as nursery:
        nursery.cancel_scope.cancel()

    h = weakref.ref(nursery)
    del nursery
    await trio.lowlevel.checkpoint()
    print(h(), gc.get_referrers(h()) if h() is not None else [])

trio.run(f)