__next__ and StopIteration

[Ian Kelly]

On Tue, Feb 10, 2015 at 9:44 AM, Ethan Furman <ethan at 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.