.py

import gc
import random
import contextlib


class Opener:
    @contextlib.contextmanager
    def open(self):
        yield random.randint(1, 100)


@contextlib.contextmanager
def make_context(obj):
    with obj.open() as val:
        del obj
        yield val


def test_referrers():
    opener = Opener()
    assert len(gc.get_referrers(opener)) == 0
    with make_context(opener) as val:
        assert len(gc.get_referrers(opener)) == 0
        del opener
        assert isinstance(val, int)


__name__ == '__main__' and test_referrers()