identity.py 文件源码

def prune(self):
        """prune unreferenced, non-dirty states."""

        ref_count = len(self)
        dirty = [s.obj() for s in self.all_states() if s.modified]

        # work around http://bugs.python.org/issue6149
        keepers = weakref.WeakValueDictionary()
        keepers.update(self)

        self._dict.clear()
        self._dict.update(keepers)
        self.modified = bool(dirty)
        return ref_count - len(self)