[Python-ideas] for/else syntax

[Gerald Britton]

Looking over this all again, it seems to me that the main request
would be for a more explicit statement in the documentation. Something
like:

"When the items are exhausted (which is immediately when the sequence
is empty), the suite in the else clause, if present, is executed, and
the loop terminates.  Note: The suite in the else clause will be
executed unless the iteration is terminated with a break or return, or
raises an exception that is not handled or does not return."

Probably it could use some word-smithing, but is that the basic idea?

One thing I DO like about the construct, though, is it makes it more
apparent what code belongs together.  e.g.

for x in y:
  # suite 1
else:
  # suite 2

It should be obvious that suite 2 belongs with the for statement in
some way.  OTOH:

for x in y:
  # suite 1

# suite 2

You can't immediately see that suite 2 is related to the for
statement.  You might think it is completely independent which could
lead to erroneous results if you modified it without keeping the
for-loop context in mind.

On Sat, Oct 3, 2009 at 1:13 PM, Masklinn <masklinn at masklinn.net> wrote:
> On 3 Oct 2009, at 18:19 , Ron Adam wrote:
>>
>> Yuvgoog Greenle wrote:
>>>
>>> Document it as much as you want but the "else" doesn't hint or clue as
>>> to whether it catches breaks or is skipped by them.
>>> The next problem's gonna be at midnight when you're reading code and
>>> asking yourself "hmmm, for, blah blah, else, hmm oh yeah, else-break,
>>> so this else occurs whenever there's a break."
>>
>> True, and that is part of the other 20% I expect the documentation would't
>> help.
>>
>> The only solution to that that I can think of is to change the esle's in
>> for and while loops to for/then and while/then in Python 5.0.
>
> That would yield
>
>    for val in vals:
>        if cond(val):
>            break
>        # processing
>    then:
>        # more stuff
>
> how does it make the "alternate" clause being skipped in case of break any
> clearer?
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-- 
Gerald Britton