[Python-ideas] SyntaxWarning for for/while/else without break or return?

[geremy condra]

On Thu, Oct 8, 2009 at 7:35 PM, Gerald Britton <gerald.britton at gmail.com>wrote:

> Ach,  I just whipped it up in a hurry.  I didn't pull it from live
> code (or even test it).   A better (working) version:
>
> >>> x = []
> >>> del i
> >>> for i, j in x:
> ...   do_something()
> ... else:
> ...   i = vars().get('i',-1)
> ...
> >>> i
> -1
> >>>
>
> And before someone says _again_ that the else is not necessary here,
> that's not the reason I use it.  I use it to structure the code so
> that it is obvious that the stuff in the else clause belongs to the
> for loop, not to code that follows it.
>
> The point is, there are valid reasons to use this construct.  That's
> just one of many, many more.  I would fight tooth-and-nail against a
> warning message, if I thought there was even the faintest chance of it
> being considered.  As it is, there is essentially no chance that it
> will be considered for the compiler (pylint is another matter,  I
> think that it _should_ be there).
>

I'm not clear- you're saying its a code smell to use it that way?

Geremy Condra


>
> On Thu, Oct 8, 2009 at 6:52 PM, Yuvgoog Greenle <ubershmekel at gmail.com>
> wrote:
> > Gerald, if this warning would have been generated you might have saved
> > yourself the mistakes on the previous thread.
> >
> > Gerald wrote as an example of "for..else" being useful without a break:
> >> for i, j in enumerate(something):
> >>  # suite
> >>  i += 1
> >> else:
> >>  i = 0
> >>
> >> # i == number of things processed
> >
> > If "# suite" has no break, "i" will always be 0. Either way after the
> > loop "i" isn't going to have the number of things processed (unless
> > "something" was empty). After being corrected Gerald wrote the
> > following remedied example:
> >
> >> for i, j in enumerate(something):
> >>  # do something
> >>  i += 1
> >> else:
> >>  i = -1
> >>
> >> if i > 0:
> >>  # we did something
> >
> > The last block "# we did something" is unreachable if "#do something"
> > has no break.
> >
> > This isn't meant to go against Gerald here btw. I'm simply saying that
> > if even the best Pythonistas can cause havoc with "for...else" then
> > think about the noobs. Personally I would suggest not using the
> > "for...break...else" idiom at all but the least we can do is give a
> > warning when "for..else" is so obviously misused.
> >
> > You could allow "break" outside of loops and simply ignore it, but you
> > don't allow it because it helps avoid bugs. Really, a warning is the
> > LEAST python can do here.
> >
> > --yuv
> >
>
>
>
> --
> Gerald Britton
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