#13814: LazyFamily.__eq__ gives false positives.
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Reporter: cnassau | Owner: sage-combinat
Type: defect | Status: needs_review
Priority: major | Milestone: sage-5.6
Component: combinatorics | Resolution:
Keywords: | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Christian Nassau | Merged in:
Dependencies: | Stopgaps:
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Comment (by cnassau):
> Should I remove the previous patch? Then we won't have to specify
> which patch to apply.
Yes, please! I would do it myself if I knew how to do it ;-)
> A couple questions:
>
> Would there be a problem to just compare the functions with:
> {{{
> self.function == other.function
> }}}
> Rather than doing the check for is and then for eq?
No problem, that's definitly better.
> I am surprised about your comment about Permutations not being
> picklable. This works for me:
> {{{
> sage: P = Permutations(3)
> sage: P == Permutations(3)
> True
> sage: P == loads(dumps(P))
> True
> }}}
This is really an issue with {{{sage.misc.fpickle}}}: the function "``n ->
Permutations(n)``" can be pickled, but the unpickled version has forgotten
the default value of the second argument of {{{Permutations(n,k)}}}:
{{{#!python
sage: f = Permutations
sage: from sage.misc.fpickle import pickle_function, unpickle_function
sage: g = unpickle_function(pickle_function(f))
sage: print f(5)
Standard permutations of 5
sage: print g(5)
Traceback (most recent call last):
...
TypeError: Permutations() takes exactly 2 arguments (1 given)
}}}
> Could the hash be calculated using both the hash of the indexing set
> and the function?
I'm now using the sum of both hashes.
> Please take the occasion to rewrite {{{WARNING}}} into
> {{{.. WARNING::}}} (see the developers manual for the exact syntax).
Fixed.
> Where is ``!=`` implemented?
That's a good question: ``grep`` could find a handful of {{{__ne__}}} in
the Sage code base, but none that would be a candidate for
{{{LazyFamily.__ne__}}}. The python manual clearly says that one should
define {{{__ne__}}} if {{{__eq__}}} is defined; that appears not to be the
case in class {{{SageObject}}}, so my guess is that Python is using a
default implementation.
By the way, both {{{Parent}}} and {{{SageObject}}} seem to test the
consistency of {{{__eq__}}} and {{{__ne__}}} in the test suite.
Cheers,\\
Christian
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13814#comment:18>
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