dict subclass and pickle bug (?)

James Stroud jstroud at mbi.ucla.edu
Fri Dec 5 11:13:49 CET 2008

Hello All,

I subclassed dict and overrode __setitem__. When instances are 
unpickled, the __setstate__ is not called before the keys are assigned 
via __setitem__ in the unpickling protocol.

I googled a bit and found that this a bug filed in 2003:


It is still "open" with "normal" priority.

Am I missing something? Is there a workaround for this bug that makes 
fixing it pointless or has it just fallen through the cracks for the 
last 5 years?

Here is an example:

class DictPlus(dict):
   def __init__(self, *args, **kwargs):
     self.extra_thing = ExtraThingClass()
     dict.__init__(self, *args, **kwargs)
   def __setitem__(self, k, v):
     do_something_with(self.extra_thing, k, v)
     dict.__setitem__(self, k, v)

Upon unpickling, the error would be:

AttributeError: 'DictPlus' object has no attribute 'extra_thing'

I'm still using python 2.5.1.


James Stroud
UCLA-DOE Institute for Genomics and Proteomics
Box 951570
Los Angeles, CA 90095


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