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Groups > comp.lang.python > #44201
| References | <kl6a1f$k2l$1@panix2.panix.com> <CAPTjJmpKR8z7Cub1WaurmsuugNgCvPYFdh9WYqJd_1OTfpLw6Q@mail.gmail.com> <CALwzidk6qz4qHOFWYqv_cDEtjbhvS_kjG0vXJZmeB0dJ07doTQ@mail.gmail.com> |
|---|---|
| Date | 2013-04-24 02:42 +1000 |
| Subject | Re: Nested iteration? |
| From | Chris Angelico <rosuav@gmail.com> |
| Newsgroups | comp.lang.python |
| Message-ID | <mailman.986.1366735371.3114.python-list@python.org> (permalink) |
On Wed, Apr 24, 2013 at 2:30 AM, Ian Kelly <ian.g.kelly@gmail.com> wrote: > On Tue, Apr 23, 2013 at 10:21 AM, Chris Angelico <rosuav@gmail.com> wrote: >> The definition of the for loop is sufficiently simple that this is >> safe, with the caveat already mentioned (that __iter__ is just >> returning self). And calling next() inside the loop will simply >> terminate the loop if there's nothing there, so I'd not have a problem >> with code like that - for instance, if I wanted to iterate over pairs >> of lines, I'd happily do this: >> >> for line1 in f: >> line2=next(f) >> print(line2) >> print(line1) >> >> That'll happily swap pairs, ignoring any stray line at the end of the >> file. Why bother catching StopIteration just to break? > > The next() there will *not* "simply terminate the loop" if it raises a > StopIteration; for loops do not catch StopIteration exceptions that > are raised from the body of the loop. The StopIteration will continue > to propagate until it is caught or it reaches the sys.excepthook. In > unusual circumstances, it is even possible that it could cause some > *other* loop higher in the stack to break (i.e. if the current code is > being run as a result of the next() method being called by the looping > construct). Ah, whoops, my bad. This is what I get for not checking. I know I've done weird stuff with for loops before, but I guess it was fiddling inside the top of it, not in its body. I love this list. If I make a mistake, it's sure to be caught by someone else. The record is guaranteed to be set straight. Thanks Ian! ChrisA
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Nested iteration? roy@panix.com (Roy Smith) - 2013-04-23 11:40 -0400
Re: Nested iteration? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 17:05 +0100
Re: Nested iteration? Ian Kelly <ian.g.kelly@gmail.com> - 2013-04-23 10:05 -0600
Re: Nested iteration? Peter Otten <__peter__@web.de> - 2013-04-23 18:15 +0200
Re: Nested iteration? Chris Angelico <rosuav@gmail.com> - 2013-04-24 02:21 +1000
Re: Nested iteration? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-23 16:35 +0000
Re: Nested iteration? Ian Kelly <ian.g.kelly@gmail.com> - 2013-04-23 10:30 -0600
Re: Nested iteration? Ian Kelly <ian.g.kelly@gmail.com> - 2013-04-23 10:39 -0600
Re: Nested iteration? Chris Angelico <rosuav@gmail.com> - 2013-04-24 02:42 +1000
Re: Nested iteration? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-04-23 16:53 +0000
Re: Nested iteration? Terry Jan Reedy <tjreedy@udel.edu> - 2013-04-23 16:49 -0400
Re: Nested iteration? Joshua Landau <joshua.landau.ws@gmail.com> - 2013-04-23 22:14 +0100
Re: Nested iteration? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 22:29 +0100
Re: Nested iteration? Joshua Landau <joshua.landau.ws@gmail.com> - 2013-04-23 22:41 +0100
Re: Nested iteration? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-04-23 23:42 +0100
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