PicklingError：无法序列化<class ...>：与...不是同一对象在GAE中

Question

我在我的GAE Python应用中遇到了一个PicklingError错误，出现在这行代码：

deferred.defer(email_voters_begin, ekey, voter_list)

这三个参数分别是：

email_voters_begin -- 这是一个Python函数，比如说，function email_voters_begin在内存中的地址是0x1035d4488
ekey -- 这是我定义的一个实体的键，比如说，它的值是agdvcGF2b3Rlcg4LEghFbGVjdGlvbhgCDA
voter_list -- 这是我定义的一个对象列表，比如说，它的内容是[models.Voter对象在内存中的地址是0x103d3d310, ... ]

当这行代码在我的测试中执行时（使用webtest和nosegae），我遇到了以下错误：

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

需要注意的是，传入deferred.defer()的Voter实体并没有BlobReference属性，但这些Voter实体确实有一个ReferenceProperty指向另一个实体，而那个实体是有BlobReference属性的。我本以为没有任何BlobInfo对象会被包含在pickle中，但错误提示似乎有一个被包含了。

当我在浏览器窗口中使用开发服务器运行相同的代码时，这个错误就不会出现。

我对如何调试这个问题感到困惑，任何建议都非常感谢。

google app engine debugging picklingerror webtest object serialization blobinfo nosegae entity key

PicklingError：无法序列化<class ...>：与...不是同一对象在GAE中

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