Hello Peter,
* Peter Bruin <pjbr...@gmail.com> [2014-05-13 07:05:43 -0700]:
> 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. I agree. We probably want to be able to unpickle these old dictionaries. Btw. you can not use an override to change the unpickling of dicts. > Do we have to create special hashable subclasses of > previously-hashable-but-now-unhashable types? That could be an option. It is not pretty but I don't see a better solution. We would have subclasses of all unhashable types which are hashable and print some deprecation warning if their __hash__ is called. If unhashable p-adics and hashable p-adics mix in a @cached_method probably strange things will happen but at least we printed a warning and told the user how to "upgrade" the old p-adics. I'll try to implement something along these lines in #11895. Thanks for the input, julian
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