On Thu, Apr 12, 2018 at 9:03 AM, Ethan Furman <et...@stoneleaf.us> wrote: > On 04/11/2018 02:55 PM, Chris Angelico wrote: >> >> On Thu, Apr 12, 2018 at 4:38 AM, Ethan Furman wrote: > >> Context managers and except blocks don't do the same thing though, so >> it's a false parallel. > > They assign things to names using `as`. Close enough. ;)
Okay, but because they don't assign the thing just before the word 'as', it's a dangerous parallel. Worse, a 'with' statement OFTEN assigns the thing just before the word 'as', making the parenthesized form frequently, but not always, the same as the unparenthesized. >> The other two are >> *dangerous* false parallels, because "with foo as bar:" is >> semantically different from "with (foo as bar):"; > > If `with` is the first token on the line, then the context manager syntax > should be enforced -- you get one or the other, not both. > That's what I had in the previous version: that 'as' bindings are straight-up not permitted in 'with' and 'except' headers. I wasn't able to implement that in the grammar, so I can't demo it for you, but the fact that this was a special case was *itself* a turn-off to some. Are special cases special enough to break the rules? Do we want something that is a subtle bug magnet? >>> - puts the calculation first, which is what we are used to seeing in >>> if/while statements; and >> >> >> Not sure what you mean here; if and while statements don't have >> anything BUT the calculation. > > Which is why we're using to seeing it first. ;) Heh. You could just as easily say you're used to seeing it next to the colon :) >> A 'for' loop puts the targets before the evaluated expression. > > Hmm, good point -- but it still uses a key word, `in`, to delineate between > the two. It does, yes. Fortunately we can't have a competing proposal for name bindings to be spelled "NAME in EXPR", because that's already a thing :D >>> - matches already existing expression-level assignments (context >>> managers, >>> try/except blocks) >> >> >> They're not expression-level assignments though, or else I'm >> misunderstanding something here? > > > No, just me being sloppy with vocabulary. > Gotcha, no problem. For myself, I've been back and forth a bit about whether "as" or ":=" is the better option. Both of them have problems. Both of them create edge cases that could cause problems. Since the problems caused by ":=" are well known from other languages (and are less serious than they would be if "=" were the operator), I'm pushing that form. However, the 'as' syntax is a close contender (unlike most of the other contenders), so if someone comes up with a strong argument in its favour, I could switch. 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/
