Exceptions while unpickling broken objects

[Patrick Gerken]

This is a weird one, unfortunately my debugging skillz failed me here.

We had a site with LinguaPlone which registers persistent utilities.
Upon removing them, we get errors when accessing the site.

This is the traceback:

2012-05-10 12:41:17 ERROR ZODB.Connection Couldn't load state for 0x156b
Traceback (most recent call last):
  File "/home/do3cc/.eggs/ZODB3-3.10.5-py2.6-linux-x86_64.egg/ZODB/Connection.py", line 860, in setstate
    self._setstate(obj)
  File "/home/do3cc/.eggs/ZODB3-3.10.5-py2.6-linux-x86_64.egg/ZODB/Connection.py", line 914, in _setstate
    self._reader.setGhostState(obj, p)
  File "/home/do3cc/.eggs/ZODB3-3.10.5-py2.6-linux-x86_64.egg/ZODB/serialize.py", line 614, in setGhostState
    state = self.getState(pickle)
  File "/home/do3cc/.eggs/ZODB3-3.10.5-py2.6-linux-x86_64.egg/ZODB/serialize.py", line 607, in getState
    return unpickler.load()
  File "/home/do3cc/v/dynajet/lib/python2.6/copy_reg.py", line 49, in _reconstructor
    obj = object.__new__(cls)
TypeError: (TypeError('object.__new__(SyncedLanguages) is not safe, use persistent.Persistent.__new__()',), <function _reconstructor at 0x7fe8f8afff50>, (<class 'Products.LinguaPlone.vocabulary.SyncedLanguages'>, <type 'object'>, None))

The SyncedLanguage class is, as expected a PersistentBroken object. Why _reconstructor tries to call object.__new__ is beyond me.
I've tried to find out who called _reconstructor, but didn't find a reasonable candidate. There is _reduce_ex, also in copy_reg like _reconstructor, but a PDB in that place never appears.
_reconstructor gets the class object, a base class and some other vars. In my pdb, I noticed that the base class was a plain object, but the method _reduce_ex would have given cls itself as a base class. So I tried to monkey patch _reconstructor to catch the TypeError and then calculate the base class like _reduce_ex does, and then just run the same code with the diffrent base class again.
This helps in our site.

Even though I patched python core libs to fix the issue, I write the issue in zodb, because it could still be zodb code thats calling the _reconstructor code here.