Currently, if I want to have weakref.finalize call an object's cleanup method, I have to do something like:

class foo:

    _finalizer = None

    def __init__(self):
        self._finalizer = weakref.finalize(self,

                                                      foo._cleanup,

                                                      weakref.WeakMethod(self.cleanup))

    def __del__(self):
        self.cleanup()

    @classmethod
    def _cleanup(cls, func):
        func()()

    def cleanup(self):
        if self._finalizer is not None:
            self._finalizer.detach()
        print('cleaning up')


It wouldn't be difficult to have weakref.finalize automatically handle the conversion to WeakMethod and automatically attempt to dereference then call the function passed in.