Question about unpickling dict subclass with custom __setstate__

Gabriel Genellina gagsl-py2 at yahoo.com.ar
Fri Sep 11 10:40:51 CEST 2009


En Thu, 10 Sep 2009 20:09:34 -0300, Matthew Wilson <matt at tplus1.com>  
escribió:

> I subclassed the dict class and added a __setstate__ method because I
> want to add some extra steps when I unpickle these entities.  This is a
> toy example of what I am doing:
>
>     class Entity(dict):
>
>         def __setstate__(self, d):
>
>             log.debug("blah...")
>
> Based on my experiments, the data in d *IS NOT* the data stored in my
> instances when I do stuff like:
>
>     e = Entity()
>     e['a'] = 1
>
> Instead, the stuff in d is the data stored when I do stuff like:
>
>     e.fibityfoo = 99

Yes. The dict contents are pickled directly; __getstate__ and __setstate__  
are related to the instance attributes (fibityfoo), not its contents  
(a->1).
Try defining __reduce__ or __reduce_ex__ instead.

> Is there anything I have to do to make sure that my real dictionary data
> is correctly reloaded during the unpickle phase?  In other words, should
> I run super(Entity, self).__setstate__(d) or something like that?

That doesn't work, dict.__setstate__ doesn't even exist.

-- 
Gabriel Genellina




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