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Re: __next__ and StopIteration

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Date Tue, 10 Feb 2015 11:54:22 +1100
Subject Re: __next__ and StopIteration
From Chris Angelico <rosuav@gmail.com>
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On Tue, Feb 10, 2015 at 11:42 AM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> Also, *technically* iterators may be re-iterable. The docs say that
> iterators which fail to raise StopIteration forever once they are exhausted
> are "broken", but the docs do not forbid broken iterators. Consenting
> adults and all that. You might want an iterator with a reset() method. Even
> an outright broken iterator!
>
>     def __next__(self):
>         if random.random() < 0.1: raise StopIteration
>         return random.random()
>
> Why you would want one, I don't know, but if you have a hankering for such a
> beast, Python lets you do it.

Yes, it is allowed. But when you write code that's documented as being
"broken", you should expect annoying, subtle errors, maybe a long way
down the track. You know all those niggling problems you get when you
find some NaNs in a series of numbers, and suddenly things don't sort
stably and such? You'll hanker for those well-defined days. :)

ChrisA

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Thread

__next__ and StopIteration Charles Hixson <charleshixsn@earthlink.net> - 2015-02-09 11:14 -0800
  Re: __next__ and StopIteration Rob Gaddi <rgaddi@technologyhighland.invalid> - 2015-02-09 19:27 +0000
  Re: __next__ and StopIteration Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-10 10:30 +1100
    Re: __next__ and StopIteration Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-09 16:56 -0700
      Re: __next__ and StopIteration Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-10 11:42 +1100
        Re: __next__ and StopIteration Chris Angelico <rosuav@gmail.com> - 2015-02-10 11:54 +1100
          Re: __next__ and StopIteration Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-10 12:11 +1100
            Re: __next__ and StopIteration Chris Angelico <rosuav@gmail.com> - 2015-02-10 12:58 +1100
        Re: __next__ and StopIteration Chris Kaynor <ckaynor@zindagigames.com> - 2015-02-09 16:59 -0800
          Re: __next__ and StopIteration Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-02-10 16:54 +1100
        Re: __next__ and StopIteration Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-10 01:30 -0700
        Re: __next__ and StopIteration Chris Kaynor <ckaynor@zindagigames.com> - 2015-02-10 09:27 -0800
    Re: __next__ and StopIteration Charles Hixson <charleshixsn@earthlink.net> - 2015-02-09 20:33 -0800
    Re: __next__ and StopIteration Chris Angelico <rosuav@gmail.com> - 2015-02-10 15:46 +1100
    Re: __next__ and StopIteration Charles Hixson <charleshixsn@earthlink.net> - 2015-02-09 22:16 -0800
    Re: __next__ and StopIteration Chris Angelico <rosuav@gmail.com> - 2015-02-10 17:38 +1100
    Re: __next__ and StopIteration Ethan Furman <ethan@stoneleaf.us> - 2015-02-10 08:44 -0800
    Re: __next__ and StopIteration Ian Kelly <ian.g.kelly@gmail.com> - 2015-02-10 09:53 -0700
    Re: __next__ and StopIteration Ethan Furman <ethan@stoneleaf.us> - 2015-02-10 09:33 -0800

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