I'm (weakly) +1 for the concept of for..else being confusing, weird, and
somehow not quite suitable/useful for many use-cases where it feels like it
should.
I'm -1 for each of the suggested improvements that I've understood so far.
I agree that the suggested 'ban' on changes in this area is probably not
helpful, however it feels like a sloppy way of saying that changes to the
syntax are very unlikely to be practical, for a couple of annoying, but
important reasons.
The:
for:
...
else: # if not break:
...
Solution seems to highlight this.
The proposed convention of using comments here is clearly elective (nothing
changes if you don't include the comment, although a style checker could
require it, which would be a nice way of catching possible indentation
errors)
Because this is implemented as a comment, and thus optional, it feels
pointless because the original confusion is still there for people who
don't bother to add the comment, and less experienced coders are less
likely to know about the convention.
BUT it's probably as good as any other changes because...
I don't feel that, on balance, the cost of making a breaking syntax change
to the language (having worked on huge python codebases, the cost of any
breaking syntax change is just massive) is justified here, so whatever
improvements may be made would probably have to still support the old
syntax as-is.
The moment we retain the old syntax, then the new syntax becomes optional,
and we're back in the problems with the comment approach.
The only route I can see to a workable outcome here is to implement the:
"else if not break:"
clause as an optional alternate syntax, and update all the documentation to
recommend using the new syntax over the old one (effectively silently
deprecate for:...else:... syntax, but retain it indefinitely).
But this has issues, because some people will still use the old syntax, so
we'll end up with lots of code out there using both variants, and that's as
likely to add to the general confusion here as reduce it.
Steve
On Wed, Jul 22, 2020 at 9:26 AM Mathew Elman <mathew.el...@ocado.com> wrote:
>
> On Wed, 22 Jul 2020 at 04:47, Paul Sokolovsky <pmis...@gmail.com> wrote:
>
>> Hello,
>>
>> On Tue, 21 Jul 2020 17:48:35 -0700
>> Christopher Barker <python...@gmail.com> wrote:
>>
>> > how about:
>> >
>> > for something in some_iterable:
>> > some_stuff_with_maybe_a_break
>> > else if not break:
>> > something_more
>> >
>> > No new keywords :-)
>> >
>> > or:
>> >
>> > for something in some_iterable:
>> > some_stuff_with_maybe_a_break
>> > else: # if not break:
>> > something_more
>>
>> This is the most genius solution posted to this thread.
>>
>> And if the thread didn't die after van Rossum's post, I don't cheer
>> hopes it would die now, but let me sprinkle in another "fresh"
>> thought. First let me remind how this thread started:
>>
>> > ELSE-clause in FOR and WHILE has unclear syntax. I suggest new clause
>> > instead
>>
>> Then various people started to throw in variants of even more unclear
>> and confusing syntax (like "if" after "for"), with some percentage of
>> those people demonstrating not understanding how the original "else"
>> works.
>>
>> But consider following idea: if it's confusing, DO NOT USE it. You
>> don't hear that often, but: treat Python as a generic programming
>> language, not as a bag of tricks. The fact that most other languages
>> don't have extra clause after "for" is enough of a reason to not use it
>> in Python either.
>>
>> The problem isn't that it is unclear, the problem is that it is
> misunderstood. If it was unclear what `for...else` means/does then yes,
> do-not-use would fix the problem. The fact that it can and *is*
> *mis*understood
> as doing something else means that people have to learn to not use
> something that feels like it *should* be usable.
>
>>
>> So why it exists at all then? It's there for people who don't find it
>> confusing, for very responsible use. As a random example, after
>> studying 2 (bytecode) Python compilers and having written my own (so I
>> know what code is generated from for-else), I no longer find it
>> confusing. I actually found 2 intuitive ways to use that construct, in
>> the very compiler mentioned - after all, if you eyeball a Python
>> compiler, you either know, or ready to learn, how all language
>> constructs work.
>>
>> For anything else - clear ban. Everyone should consider that too. (But
>> please leave the language syntax alone (backwards compatibility, etc.),
>> at least that's a suggestion which comes out from van Rossum's post).
>
>
>
> Frankly, saying that a part of a language that is frequently
> misunderstood, is *never* allowed to be improved is disappointing when
> the suggestion that it can be (somehow) has been so well received by
> everyone else.
>
>
>>
>> > As for the "loop didn't run at all" case: Does anyone find a need for
>> > that? Personally, I've found that everytime I do some kind of check
>> > for an empty iterable before a loop, it was totally unnecessary.
>>
>> I find the need for that regularly. And I use the obvious syntax which
>> everyone else uses:
>>
>> if not seq:
>> print("This page is intentionally left blank")
>> else:
>> for i in seq:
>> ...
>>
>> Any adhoc, confusing syntax someone may imagine to add, would go to the
>> same "DO NOT USE" category. So, I pray to van Rossum's answer that
>> something like that will never be added to the language. (Which is
>> hard to hang hopes on, given all the mess added recently.)
>
>
> Many people offering approaches is not muddling the thread. Clearly, most
> people here agree that `for...else` is confusing/unintuitive on it's own,
> and could be improved (not removed, but improved). The discussion was
> trying to find an improvement that people agree on as well. The reason
> there are so many offerings, is probably because everyone has had a similar
> thought about it in the past.
>
>
> Notice:
> This email is confidential and may contain copyright material of members
> of the Ocado Group. Opinions and views expressed in this message may not
> necessarily reflect the opinions and views of the members of the Ocado
> Group.
>
> If you are not the intended recipient, please notify us immediately and
> delete all copies of this message. Please note that it is your
> responsibility to scan this message for viruses.
>
> References to the "Ocado Group" are to Ocado Group plc (registered in
> England and Wales with number 7098618) and its subsidiary undertakings (as
> that expression is defined in the Companies Act 2006) from time to time.
> The registered office of Ocado Group plc is Buildings One & Two, Trident
> Place, Mosquito Way, Hatfield, Hertfordshire, AL10 9UL.
> _______________________________________________
> Python-ideas mailing list -- python-ideas@python.org
> To unsubscribe send an email to python-ideas-le...@python.org
> https://mail.python.org/mailman3/lists/python-ideas.python.org/
> Message archived at
> https://mail.python.org/archives/list/python-ideas@python.org/message/VLKG6NE4DOX43NZIHSTSSV5POM6AZ2NQ/
> Code of Conduct: http://python.org/psf/codeofconduct/
>
_______________________________________________
Python-ideas mailing list -- python-ideas@python.org
To unsubscribe send an email to python-ideas-le...@python.org
https://mail.python.org/mailman3/lists/python-ideas.python.org/
Message archived at
https://mail.python.org/archives/list/python-ideas@python.org/message/OZJ74BEHUWX6SZTVAZOGV43T6ABUPIWQ/
Code of Conduct: http://python.org/psf/codeofconduct/
