[Python-Dev] Adding an rslice() builtin?

[David Hopwood]

Nick Coghlan wrote:
> A discussion on the py3k list reminded me that translating a forward slice 
> into a reversed slice is significantly less than obvious to many people. Not 
> only do you have to negate the step value and swap the start and stop values, 
> but you also need to subtract one from each of the step values, and ensure the 
> new start value was actually in the original slice:
> 
>    reversed(seq[start:stop:step]) becomes seq[(stop-1)%abs(step):start-1:-step]
> 
> An rslice builtin would make the latter version significantly easier to read:
> 
>    seq[rslice(start, stop, step)]

Or slice.reversed().

-- 
David Hopwood <david.nospam.hopwood at blueyonder.co.uk>