If alive then mark as dead and return (obj, func, args, kwargs);
        otherwise return None

def detach(self):
        """If alive then mark as dead and return (obj, func, args, kwargs);
        otherwise return None"""
        info = self._registry.get(self)
        obj = info and info.weakref()
        if obj is not None and self._registry.pop(self, None):
            return (obj, info.func, info.args, info.kwargs or {})