On Fri, 18 Sep 2015 10:47 pm, Random832 wrote: > On Fri, Sep 18, 2015, at 08:30, Steven D'Aprano wrote: >> On Fri, 18 Sep 2015 07:26 am, Random832 wrote: >> >> > I don't even think chaining should >> > work for all *actual* comparison operations. >> >> I don't see why. Mathematicians chain comparisons all the time. If the >> language implements the same semantics as mathematicians already use, why >> do you dislike that? > > Please provide a citation for this claim.
Really? You're disputing that chained comparisons are a standard maths notation? https://en.wikipedia.org/wiki/Inequality_(mathematics)#Chained_notation Mathworld, for example, says: Solutions to the inequality |x-a|<b consist of the set {x:-b<x-a<b}, or equivalently {x:a-b<x<a+b}. http://mathworld.wolfram.com/Inequality.html >> Only if the comparisons are transitive, which they may not be. > > My *entire point* is that it *shouldn't be used* for non-transitive > comparisons!!! And my point is that there is no good reason for such a restriction, even if it were technically possible to enforce (which it is not). The mathematical chained notation doesn't rely on, or imply, transitivity. Given a < b < c, *if* the operator is transitive, then AND ONLY THEN can you conclude that a < c, but that's not implied by the chaining. It happens to be true for real numbers, but it isn't necessarily true. -- Steven -- https://mail.python.org/mailman/listinfo/python-list
