python-gc.py

import weakref
import gc

class Foo:
    def __init__(self, factory):
        self.factory = factory

class Factory:
    def mk_foo(self):
        self.foo = Foo(self)
        return self.foo

def test_me():
    f = Factory()
    foo = weakref.proxy(f.mk_foo())

    del f
    gc.collect()
    print(str(foo))

if __name__ == "__main__":
    test_me()