PicklingError:无法pickle<class…>：它与。。。在GAE

Question

我在GAE Python应用程序的这行代码中得到一个PicklingError：

deferred.defer(email_voters_begin, ekey, voter_list)

这三个论点是：

• 电子邮件选民开始——一个Python函数，例如，函数email选民开始于0x1035d4488
• ekey——我定义的实体的键，例如，打印为agdvcGF2b3Rlcg4LEghFbGVjdGlvbhgCDA
• 投票者列表——我定义的对象列表，例如，[位于0x103D310的models.voter对象。。。]

当这一行作为测试的一部分执行时（使用webtest和nosegae），我得到以下错误：

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，传入deferred.defer()的Voter实体没有BlobReference属性，但是Voter实体对另一个具有BlobReference属性的实体具有ReferenceProperty属性。我不认为任何BlobInfo对象都是pickle的一部分，但错误表明其中包含一个对象。

当我使用dev服务器从浏览器窗口运行相同的代码时，不会发生此错误。

我很困惑如何调试这个和任何想法将非常感谢。

Answer 1

这可能是因为您已经在至少一个投票者对象上检索了ReferenceProperty。一旦取消引用ReferenceProperty，模型实例就会缓存它。Pickling也会pickle任何缓存对象，因此它会尝试序列化Voter实例、引用实例及其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，则将实例序列化到协议缓冲区，然后发送这些实例。

Answer 2

您不应该将模型实例传递给延迟的。改为使用密钥：

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

在您的电子邮件中，选民开始：

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