Python中的酸洗弱引用

Question

我仍然是Python的新手，甚至是酸菜的新手。我有一个带有__getnewargs__()的Vertex(ScatterLayout)类

def __getnewargs__(self):
    return (self.pos, self.size, self.idea.text)

我的理解是，这将导致pickle从__getnewargs__()而不是对象的字典中pickle对象。

pickle在以下方法中调用(在不同的类MindMapApp(App)中)：

def save(self):
    vertices = self.mindmap.get_vertices()
    edges = self.mindmap.get_edges()

    output = open('mindmap.pkl', 'wb')

    #pickle.dump(edges, output, pickle.HIGHEST_PROTOCOL)
    pickle.dump(vertices, output, pickle.HIGHEST_PROTOCOL)

    output.close()

当我调用save()方法时，我得到以下错误：

pickle.PicklingError: Can't pickle <type 'weakref'>: it's not found as __builtin__.weakref

我遗漏了什么或不理解什么？我还尝试实现了__getstate__() / __setstate__(state)组合，并获得了相同的结果。

Answer 1

你绝对可以腌制weakref，你也可以腌制dict和list。然而，它们所包含的内容实际上很重要。如果dict或list包含任何不可拾取的项，则酸洗将失败。如果你想要weakref，你必须使用dill，而不是pickle。然而，未酸洗的weakref反序列化为死引用。

>>> import dill
>>> import weakref
>>> dill.loads(dill.dumps(weakref.WeakKeyDictionary()))
<WeakKeyDictionary at 4528979192>
>>> dill.loads(dill.dumps(weakref.WeakValueDictionary()))
<WeakValueDictionary at 4528976888>
>>> class _class:
...   def _method(self):
...     pass
... 
>>> _instance = _class()
>>> dill.loads(dill.dumps(weakref.ref(_instance)))
<weakref at 0x10d748940; dead>
>>> dill.loads(dill.dumps(weakref.ref(_class())))
<weakref at 0x10e246a48; dead>
>>> dill.loads(dill.dumps(weakref.proxy(_instance)))
<weakproxy at 0x10e246b50 to NoneType at 0x10d481598>
>>> dill.loads(dill.dumps(weakref.proxy(_class())))
<weakproxy at 0x10e246ba8 to NoneType at 0x10d481598>

Answer 2

我通过在__getstate__/__setstate__中的弱/强引用之间切换来解决此问题

class DBObject(object):
    def __getstate__(self):
        s = self.__dict__.copy()
        s['_db'] = s['_db']()
        return s

    def __setstate__(self, state):
        self.__dict__ = state.copy()
        self.__dict__['_db'] = weakref.ref(self.__dict__['_db'])