Python pickling error when using sessions

In my django app I was creating an extended user profile using session vars. But when registration form was saved and user was about to create, I got following error :

Traceback (most recen开发者_开发百科t call last):

  File "\Python26\Lib\site-packages\django\core\servers\basehttp.py", line 279, in run
    self.result = application(self.environ, self.start_response)

  File "\Python26\Lib\site-packages\django\core\servers\basehttp.py", line 651, in __call__
    return self.application(environ, start_response)

  File "\Python26\Lib\site-packages\django\core\handlers\wsgi.py", line 245, in __call__
    response = middleware_method(request, response)

  File "\Python26\Lib\site-packages\django\contrib\sessions\middleware.py", line 36, in process_response
    request.session.save()

  File "\Python26\Lib\site-packages\django\contrib\sessions\backends\db.py", line 53, in save
    session_data = self.encode(self._get_session(no_load=must_create)),

  File "\Python26\Lib\site-packages\django\contrib\sessions\backends\base.py", line 88, in encode
    pickled = pickle.dumps(session_dict, pickle.HIGHEST_PROTOCOL)

PicklingError: Can't pickle <type 'cStringIO.StringO'>: attribute lookup cStringIO.StringO failed

I've googled for an answer, but found nothing interesting. Any workarounds for this ?

It appears you have a cStringIO object in your session (perhaps an uploaded file?), these cannot be pickled. Either write custom pickling code or make sure all your session data can be serialized.

Something weird going on here, because the error refers to cStringIO.StringO whereas the class is actually cStringIO.StringIO, with an extra I. Have you misspelled the name somewhere?

In support of Ivo's answer, here's a reference I found which may explain this: http://bugs.python.org/issue5345

This is not a typo. cStringIO.StringIO is a factory function that returns either a cStringO object (for writing) or cStringI (for reading). If this behavior causes a problem to you, then consider using StringIO.StringIO.

Alternatively, you could upgrade to Python 2.7 or 3.0 and use io.StringIO() which doesn't have this limitation.