python - PicklingError : Can't pickle : it's not the same object as . .. 在 GAE 中

Question

我从我的 GAE Python 应用程序中的这行代码中收到 PicklingError:

deferred.defer(email_voters_begin, ekey, voter_list)

这三个参数是:

• email_voters_begin -- 一个 Python 函数，例如位于 0x1035d4488 的函数 email_voters_begin
• ekey -- 我定义的实体的 key ，例如，打印为 agdvcGF2b3Rlcg4LEghFbGVjdGlvbhgCDA
• voter_list -- 我定义的对象列表，例如，[models.Voter 对象位于 0x103d3d310, ... ]

当此行作为我的测试的一部分执行时(使用 webtest 和 nosegae)，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，deferred.defer() 中传递的 Voter 实体没有 BlobReference 属性，但 Voter 实体确实具有指向另一个具有 BlobReference 属性的实体的 ReferenceProperty 属性。我不认为任何 BlobInfo 对象都会成为 pickle 的一部分，但错误表明其中包含一个对象。

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。

我对如何调试这个感到困惑，任何想法将不胜感激。

Answer 1

发生这种情况的原因可能是您已检索至少一个 Voter 对象的 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 指出的那样，将模型实例传递给 deferred 通常不是一个好主意。如果可能，请发送 key ，如果没有，请将实例序列化到 Protocol Buffer 并发送它们。