On Tue, Jun 23, 2020 at 4:41 PM MRAB <pyt...@mrabarnett.plus.com> wrote:
> On 2020-06-23 22:50, Barry Warsaw wrote: > > On Jun 23, 2020, at 14:31, Chris Angelico <ros...@gmail.com> wrote: > > > >> I can't find it among the rejected alternatives, but was it considered > >> to use "..." as the wildcard, rather than "_"? It carries similar > >> meaning but its special case of "this will never be bound" is simply > >> preventing an error, rather than making one otherwise-valid name > >> special. > > > > I thought of that too as I was reading the PEP, but forgot to add it to > my notes. I do like ellipsis more than underscore here. > > > +1 > The problem is that ellipsis already has a number of other meanings, *and* is easily confused in examples and documentation with leaving things out that should be obvious or uninteresting. Also, if I saw [a, ..., z] in a pattern I would probably guess that it meant "any sequence of length > 2, and capture the first and last element" rather than "a sequence of length three, and capture the first and third elements". (The first meaning is currently spelled as [a, *_, z].) So I'm not a fan. _ is what all other languages with pattern matching seem to use, and I like that case (x, _, _) resembles the use of (x, _, _) in assignment targets. > However, what if you wanted to match Ellipsis? > > This could lead to bugs: > > >>> ... > Ellipsis > >>> Ellipsis = 0 > >>> Ellipsis > 0 > >>> ... > Ellipsis > Now you're just being silly. If you want to use Ellipsis as a variable you can't also use it to refer to the "..." token. > If you can have "case False:" and "case True:", should 'Ellipsis' become > a keyword so that you could have "case Ellipsis:"? Or do they have to be > "case .False:", "case .True:", in which case it could remain "case > .Ellipsis:"? > I don't think this problem is at all bad enough to make "Ellipsis" a keyword. It is much, much less used than True, False or None. -- --Guido van Rossum (python.org/~guido) *Pronouns: he/him **(why is my pronoun here?)* <http://feministing.com/2015/02/03/how-using-they-as-a-singular-pronoun-can-change-the-world/>
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