[Python-ideas] Where did we go wrong with negative stride?

[Nick Coghlan]

On 30 October 2013 20:02, Paul Moore <p.f.moore at gmail.com> wrote:
> On 30 October 2013 09:52, Oscar Benjamin <oscar.j.benjamin at gmail.com> wrote:
>> Firstly would it not be better to add slice.__reversed__ so that it would be
>>
>>     b = a[reversed(slice(i, j))]
>
> This won't work, because reversed returns an iterator, not a slice object.
>
>> Secondly I don't think I would ever actually want to use this over the
>> existing possibilities.
>
> Agreed, while my usage is pretty trivial, I would definitely use
>
>     b = a[::-1]
>
> over
>
>     b = a[Slice(None, None, None, reversed=True)]
>
> I could probably omit some of those None arguments, but I probably
> wouldn't simply because I can't remember which are optional.

Why does that give you trouble when it's identical to what you can
omit from the normal slice syntax? (and from range)


>> There are real problems with slicing and indexing in Python that lead
>> to corner cases and bugs but this particular issue is not one of them.
>> The real problems, including the motivating example at the start of
>> this thread, are caused by the use of negative indices to mean from
>> the end.

And this is one of the things my rslice recipe handles correctly.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia