Hi Julian,
OK, I see the problem. It seems that it is not unique to DirichletGroup,
but is more general:
sage: class pAdicNumber(object): pass
sage: d = { pAdicNumber(): 0 }
sage: s = dumps(d)
sage: pAdicNumber.__hash__ = None
sage: loads(s)
...
TypeError: unhashable type: 'pAdicNumber'
For all we know, old pickles everywhere (e.g. on people's computers, not in
the pickle jar) may contain dictionaries where p-adic numbers are used as
keys. What to do about this? It sounds a bit drastic to generally change
unpickling of dictionaries so that keys whose type is unhashable are
silently dropped. Do we have to create special hashable subclasses of
previously-hashable-but-now-unhashable types?
Peter
Op dinsdag 13 mei 2014 12:46:56 UTC+1 schreef Julian Rüth:
>
> Thanks for your answers.
>
> * Peter Bruin <[email protected] <javascript:>> [2014-05-13 01:23:56
> -0700]:
>
> > Here is my solution to a similar problem in #15158:
> >
> > def __setstate__(self, state):
> The problem is that __setstate__ never gets called because the error
> happens earlier, during the unpickling of state.
> In other words, if I change DirichletGroup to
>
> sage: class DirichletGroup(object):
> ....: def __setstate__(self, state):
> ....: assert(False) # I never get here
>
> then the assertion is not triggered by loads(s).
>
> julian
>
> > Op dinsdag 13 mei 2014 03:16:28 UTC+1 schreef Julian Rüth:
> > >
> > > Hello sage-devel,
> > >
> > > at #11895 I'm trying to make p-adic numbers unhashable. This works
> > > nicely except for one pickle from the pickle jar that I can't seem to
> > > fix.
> > >
> > > The problem is that DirichletGroup_class used to have a dict which
> uses
> > > p-adic numbers as keys. That dict used to be a cache which is not used
> > > anymore, so dropping it would be no problem. However, I can only drop
> it
> > > after the dict has been unpickled. But this fails since the unhashable
> > > p-adic numbers can not be used as keys anymore.
> > >
> > > Here is a minimal example to illustrate the problem:
> > >
> > > sage: class DirichletGroup(object): pass
> > > sage: class pAdicNumber(object): pass # the old hashable p-adic number
> > > sage:
> > > sage: G = DirichletGroup()
> > > sage: G._cache = { pAdicNumber() : 0 }
> > > sage: s = dumps(G)
> > > sage:
> > > sage: class pAdicNumber(object):
> > > ....: __hash__ = None # now p-adics are not hashable anymore
> > > ....:
> > > sage: loads(s)
> > > TypeError: unhashable type: 'pAdicNumber'
> > >
> > > Any ideas how I could influence the unpickling so that the string s
> can
> > > be unpickled with the _cache dropped in this example?
> > >
> > > Thanks,
> > >
> > > julian
> > >
> >
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