[Python-Dev] PEP for adding an sq_index slot so that any object, a or b, can be used in X[a:b] notation

Thu Feb 9 09:46:12 CET 2006

Travis Oliphant wrote:
> PEP: ###
> Title: Allowing any object to be used for slicing
> [...]
> Rationale
>> Currently integers and long integers play a special role in slice
> notation in that they are the only objects allowed in slice
> syntax. In other words, if X is an object implementing the sequence
> protocol, then X[obj1:obj2] is only valid if obj1 and obj2 are both
> integers or long integers. There is no way for obj1 and obj2 to
> tell Python that they could be reasonably used as indexes into a
> sequence. This is an unnecessary limitation.
> [...]

I like the general idea from an academic point of view.
Just one question: could you explain what I should expect from x[ 
slicer('spam') : slicer('eggs') ] when slicer implements this 
protocol?
Specifically, I'd like to known how you want to define the interval 
between two objects. Or is that for the sliced/indexed object to 
decide?
--eric