dict subclass and pickle bug (?)
Terry Reedy
tjreedy at udel.edu
Fri Dec 5 12:55:53 EST 2008
James Stroud wrote:
> James Stroud wrote:
>> 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 an 'issue' reporting a possibly unexpected side-effect of protocol
working as designed and documented. Possibly a design flaw, but not a
bug in the narrow sense (in spite of the url of the issue tracker).
>> http://bugs.python.org/issue826897
>>
>> It is still "open" with "normal" priority.
>
> Here is the ugly "fix" I'm basically going to have to live with, it seems:
>
> class DictPlus(dict):
> def __init__(self, *args, **kwargs):
> self.extra_thing = ExtraThingClass()
> dict.__init__(self, *args, **kwargs)
> def __setitem__(self, k, v):
> try:
> do_something_with(self.extra_thing, k, v)
> except AttributeError:
> self.extra_thing = ExtraThingClass()
> do_something_with(self.extra_thing, k, v)
> dict.__setitem__(self, k, v)
> def __setstate__(self, adict):
> pass
I took the liberty of adding this to the issue.
> I can't imagine this bug has survived
because there is no bug to fix. I have suggesting closing.
Terry Jan Reedy
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