#8119: Rename change the hash value of some objects
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Reporter: hivert | Owner: tbd
Type: defect | Status: needs_review
Priority: major | Milestone: sage-4.3.4
Component: misc | Keywords:
Author: | Upstream: N/A
Reviewer: | Merged:
Work_issues: |
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Comment(by robertwb):
Replying to [comment:3 hivert]:
> Hi Robert,
>
> I've one question related to this and I like to have the confirmation
from an expert. After your patch, upon pickling/unpickling the hash value
can change because it is not pickled and neither is the name, right ? As
far as I manage to test this is not harmful to pickle a dict containing a
renamed parent. Indeed, trying to read {{{cPickle.c}}}, I understood that
the dict is reconstructed from it's items and thus even if the hash
changed the element is inserted correctly in the dict during unpickling.
Can you confirm this ?
That is correct. Hashes in general are not guaranteed to be consistent
from run to run, all that really matters is that they satisfy (to the best
they can) the equality constraints.
> If this is not both this patch and #8120 are broken.
>
> Also, after this, do you still need #8506 ?
Yes, #8506 is still important--in my case I'm reducing a curve mod many,
many primes, doing just a bit of stuff on each before throwing them away.
I suppose eventually caching the hash value would eventually be a win, but
that's a separate optimization.
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/8119#comment:4>
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