PicklingError: Can't pickle <class ...>: it's not the same object as ... in GAE答案

【问题标题】：PicklingError: Can't pickle <class ...>: it's not the same object as ... in GAEPicklingError: Can't pickle <class ...>: it's not the same object as ... in GAE
【发布时间】：2012-01-23 02:38:56
【问题描述】：

我的 GAE Python 应用程序中的这行代码出现 PicklingError：

deferred.defer(email_voters_begin, ekey, voter_list)

三个参数是：

email_voters_begin -- Python 函数，例如，函数 email_voters_begin 位于 0x1035d4488
ekey -- 我定义的实体的密钥，例如，打印为 agdvcGF2b3Rlcg4LEghFbGVjdGlvbhgCDA
voter_list -- 我定义的对象列表，例如 [models.Voter object at 0x103d3d310, ...]

当此行作为我的测试的一部分（使用 webtest 和 nosegae）执行时，我收到以下错误：

Traceback (most recent call last):
  [...]
  File "/Users/joneill/OpenSTV/OpenSTV/trunk/OpaVote-HR/tasks.py", line 29, in init_voters_and_send_email
    deferred.defer(email_voters_begin, ekey, voter_list)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/deferred/deferred.py", line 249, in defer
    pickled = serialize(obj, *args, **kwargs)
  File "/Applications/GoogleAppEngineLauncher.app/Contents/Resources/GoogleAppEngine-default.bundle/Contents/Resources/google_appengine/google/appengine/ext/deferred/deferred.py", line 221, in serialize
    return pickle.dumps(curried, protocol=pickle.HIGHEST_PROTOCOL)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 1374, in dumps
    Pickler(file, protocol).dump(obj)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 224, in dump
    self.save(obj)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  [...]
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 331, in save
    self.save_reduce(obj=obj, *rv)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 396, in save_reduce
    save(cls)
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 286, in save
    f(self, obj) # Call unbound method with explicit self
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/pickle.py", line 753, in save_global
    (obj, module, name))
PicklingError: Can't pickle <class 'google.appengine.ext.blobstore.blobstore.BlobInfo'>: it's not the same object as google.appengine.ext.blobstore.blobstore.BlobInfo

请注意，在deferred.defer() 中传递的Voter 实体没有BlobReference 属性，但Voter 实体确实具有ReferenceProperty 到另一个具有BlobReference 属性的实体。我认为任何 BlobInfo 对象都不会成为泡菜的一部分，但错误表明其中包含一个。

当我使用开发服务器从浏览器窗口运行相同的代码时，不会发生此错误。

我不知道如何调试它，任何想法都将不胜感激。

【问题讨论】：

标签： python google-app-engine pickle

【解决方案1】：

这很可能是因为您在至少一个 Voter 对象上检索到了ReferenceProperty。一旦取消引用 ReferenceProperty，模型实例就会缓存它。 Pickling 也会腌制任何缓存的对象，因此它会尝试序列化 Voter 实例、引用的实例及其 BlobInfo。

一般来说，正如 Skirmantas 所指出的，将模型实例传递给 deferred 通常是个坏主意。在可能的情况下，发送密钥，如果没有，将实例序列化到协议缓冲区并发送它们。

【讨论】：

【解决方案2】：

您永远不应该将模型实例传递给 deferred。改用键：

deferred.defer(email_voters_begin, ekey, [v.key() for v in voter_list])

在您的 email_voters_begin 中：

def email_voters_begin(ekey, voters_keys):
    voter_list = models.Voter.get(voters_keys)

【讨论】：