#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 nthiery):
Replying to [comment:10 cnassau]:
> This has some really bad consequences if (as I believe) we're __not__
able to reliably test functions for equality. We would then have to live
with
>
> {{{
> sage: LazyFamily([1,2,3], lambda i:i) == LazyFamily([1,2,3], lambda
i:i)
> False
> }}}
That is perfectly fine for me: if the caller asked explicitly for a
lazy family, then (s)he should expect the comparison to be lazy, and
thus cheap but incomplete. If she is willing to pay the price of
computing the function on all indices, then a FiniteFamily is what she
wants.
> As noted in `src/categories/enumerated_sets.py` a set can choose to not
implement `list` if it is probably too large to be useful.
Yup. But there are a lot of sets, like Permutations(n) that can be
very small or very large, and such sets cannot make a good decision.
At the end of the day, it's better to take the decision upon building
the family (by asking explicitly for a lazy family or not).
> I've changed my mind: this is not at all a good idea: in my tests an
`unpickle_function(lambda i:i)` includes a reference to the doctest where
it was defined. That's not good at all if we want to test for function
equality... for similar reasons it seems bad to use the bytecode
disassembly from the dis module...
Ok!
Kind regards,
Nicolas
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/13814#comment:11>
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