Re: [sage-devel] A issue with the Set function in sage
> >> - the problem is that lists are not hashable, and considered unequal. >> The problem is that in general testing objects for equality is far >> from obvious, might be algorithmically unsolvable, etc. >> >> Why is Set trying then? I can see in the documentation that "Sets with > unhashable objects work, but with less functionality", but as this example > shows, it's more "but with misleading functionality". How is this ever > useful? > > Because sometimes you need to have something that is a Sage object in a category. Also sometimes you want a set-like object with unhashable things. However, I agree that it should try a bit harder to remove redundant elements by a brute force check. > sage: a,b=list(Set([[0],[0]])) > sage: a==b > True > > I don't know if this is ever useful internally (I doubt it; I expect it > mainly makes bugs harder to find), but we should definitely not be exposing > this as user interface, Python's own "frozenset" and "set" are better > behaved. > +1 for general internal use. However, set and frozenset can behave quite differently than over objects in Sage, and something dealing with that nonuniformity leads to more cases and code. Best, Travis -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/9ebed824-3c12-4dc0-90e7-857d7dd29520o%40googlegroups.com.
Re: [sage-devel] A issue with the Set function in sage
See https://trac.sagemath.org/ticket/23324 for some discussion. Am Donnerstag, 25. Juni 2020 19:19:26 UTC+2 schrieb Nils Bruin: > > > > On Thursday, June 25, 2020 at 5:00:23 AM UTC-7, Dima Pasechnik wrote: >> >> >> - the problem is that lists are not hashable, and considered unequal. >> The problem is that in general testing objects for equality is far >> from obvious, might be algorithmically unsolvable, etc. >> >> Why is Set trying then? I can see in the documentation that "Sets with > unhashable objects work, but with less functionality", but as this example > shows, it's more "but with misleading functionality". How is this ever > useful? > > sage: a,b=list(Set([[0],[0]])) > sage: a==b > True > > I don't know if this is ever useful internally (I doubt it; I expect it > mainly makes bugs harder to find), but we should definitely not be exposing > this as user interface, Python's own "frozenset" and "set" are better > behaved. > -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/2cc7f9b1-f3e9-4e9d-8f66-8ba93f7d0c8do%40googlegroups.com.
Re: [sage-devel] A issue with the Set function in sage
On Thursday, June 25, 2020 at 5:00:23 AM UTC-7, Dima Pasechnik wrote: > > > - the problem is that lists are not hashable, and considered unequal. > The problem is that in general testing objects for equality is far > from obvious, might be algorithmically unsolvable, etc. > > Why is Set trying then? I can see in the documentation that "Sets with unhashable objects work, but with less functionality", but as this example shows, it's more "but with misleading functionality". How is this ever useful? sage: a,b=list(Set([[0],[0]])) sage: a==b True I don't know if this is ever useful internally (I doubt it; I expect it mainly makes bugs harder to find), but we should definitely not be exposing this as user interface, Python's own "frozenset" and "set" are better behaved. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/ae7e774b-3921-4a11-9c6c-63aec90d0e05o%40googlegroups.com.
Re: [sage-devel] A issue with the Set function in sage
On Thu, Jun 25, 2020 at 12:49 PM Ars-Magna wrote: > > Is the following a bug ? > > sage: Set([[(Integer(0), Integer(0)), (Integer(1), Integer(1))],[(Integer(0), > Integer(0)), (Integer(1), Integer(1))]]).cardinality() > > 2 hard to say. Note that sage: Set([[(0,0), (1,1)],[(0,0), (1,1)]]).cardinality() 2 sage: Set([((0,0), (1,1)),((0,0), (1,1))]).cardinality() 1 and even sage: Set([[0],[0]]).cardinality() 2 - the problem is that lists are not hashable, and considered unequal. The problem is that in general testing objects for equality is far from obvious, might be algorithmically unsolvable, etc. > > -- > You received this message because you are subscribed to the Google Groups > "sage-devel" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sage-devel+unsubscr...@googlegroups.com. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sage-devel/4c7163cb-84c5-4bf0-9ef3-585e709883b7o%40googlegroups.com. -- You received this message because you are subscribed to the Google Groups "sage-devel" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-devel+unsubscr...@googlegroups.com. To view this discussion on the web visit https://groups.google.com/d/msgid/sage-devel/CAAWYfq3R8D_jyQEJCZeWtEmZGQJmTR8xu5%3DKbnUeRUhttdB%3Dmg%40mail.gmail.com.
