On Fri, Apr 13, 2018 at 10:22 PM, Steven D'Aprano <st...@pearwood.info> wrote: > On Wed, Apr 11, 2018 at 11:50:44PM +1000, Chris Angelico wrote: > >> > Previously, there was an alternative _operator form_ `->` proposed by >> > Steven D'Aprano. This option is no longer considered? I see several >> > advantages with this variant: >> > 1. It does not use `:` symbol which is very visually overloaded in Python. >> > 2. It is clearly distinguishable from the usual assignment statement and >> > it's `+=` friends >> > There are others but they are minor. >> >> I'm not sure why you posted this in response to the open question, but >> whatever. The arrow operator is already a token in Python (due to its >> use in 'def' statements) and should not conflict with anything; >> however, apart from "it looks different", it doesn't have much to >> speak for it. > > On the contrary, it puts the expression first, where it belongs > *semi-wink*.
The 'as' syntax already has that going for it. What's the advantage of the arrow over the two front-runners, ':=' and 'as'? > The expression is the most important part of the assignment expression, > and because we read from left to right, it should come first. Let's take > a simple example: > > pair = (first_value := x + y + z, > a + b + first_value > ) > > What's the first item of the pair? If you're like me, and I think most > people are similar, when skimming the code, you read only far across > each line to get an idea of whether it is relevant or not. Yet Python has an if/else operator that, in contrast to C-inspired languages, violates that rule. So it's not a showstopper. :) >> The arrow faces the other way in languages like Haskell, > > Indeed, but in R, it faces to the right. (Actually, R allows both > direction.) There's also apparently a language BETA which uses -> for > assignment, although I've never used it. I looked up R's Wikipedia page and saw only the left-facing arrow. How common is the right-facing arrow? Will people automatically associate it with name binding? > HP calculator "RPN" language also includes a -> assignment operator for > binding named parameters (taken off the stack) inside functions, except > they use a custom encoding with an arrow symbol, not a literal > hyphen+greater-than sign. > > Likewise for TI Nspire calculators, which also use an right-pointing > arrow assignment operator. (They also have a Pascal-style := operator, > so you're covered both ways.) This comes from various dialects of > calculator BASIC. So we have calculators, and possibly R, and sorta-kinda Haskell, recommending some form of arrow. We have Pascal and its derivatives recommending colon-equals. And we have other usage in Python, with varying semantics, recommending 'as'. I guess that's enough to put the arrow in as another rejected alternate spelling, but not to seriously consider it. ChrisA _______________________________________________ Python-ideas mailing list Python-ideas@python.org https://mail.python.org/mailman/listinfo/python-ideas Code of Conduct: http://python.org/psf/codeofconduct/
