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Re: __next__ and StopIteration

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From Ian Kelly <ian.g.kelly@gmail.com>
Date Tue, 10 Feb 2015 09:53:57 -0700
Subject Re: __next__ and StopIteration
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On Tue, Feb 10, 2015 at 9:44 AM, Ethan Furman <ethan@stoneleaf.us> wrote:
> On 02/09/2015 08:46 PM, Chris Angelico wrote:
>>
>> class Grid:
>>     blah blah
>>
>>     def __iter__(self):
>>         for row in range(self._rows):
>>             for col in range(self._cols):
>>                 if self._grid[row][col]:
>>                     yield self._grid[row][col]
>
> I strongly suggest you remove the
>
>   if self._grid[row][col]:
>
> line.
>
> Best case scenario: the entire grid is blank, and iterating through it does nothing.
>
> Worst case scenario:  only some elements evaluate as False, so your loop doesn't execute the full number of times; i.e.
> with a grid of 4x5 with 7 blank cells you get 13 iterations -- probably not what was expected.

Depends on what the expected behavior is -- is every grid position
something that should be included in the iteration, or are we looking
at elements of a container where some possible locations may be empty?
You don't expect a dict iteration to yield empty buckets, for example.

I have some code that looks similar to this, which is an iterator for
a chess board that yields the contained pieces. It doesn't really make
sense in that case to yield empty squares.

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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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