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

[Travis E. Oliphant]

Guido van Rossum wrote:
> On 2/9/06, Travis Oliphant <oliphant.travis at ieee.org> wrote:
> 
> 
> BTW do you also still want to turn ZeroDivisionError into a warning
> (that is changed into an error by default)? That idea shared a slide
> and I believe it was discussed in the same meeting you & I and some
> others had in San Mateo last summer.

I think that idea has some support, but I haven't been thinking about it 
for awhile.

> 
> 
> Shouldn't this slot be in the PyNumberMethods extension? It feels more
> like a property of numbers than of a property of sequences. Also, the
> slot name should then probably be nb_index.

Yes, definitely!!!

> 
> There's also an ambiguity when using simple indexing. When writing
> x[i] where x is a sequence and i an object that isn't int or long but
> implements __index__, I think i.__index__() should be used rather than
> bailing out. I suspect that you didn't think of this because you've
> already special-cased this in your code -- when a non-integer is
> passed, the mapping API is used (mp_subscript). This is done to
> suppose extended slicing. The built-in sequences (list, str, unicode,
> tuple for sure, probably more) that implement mp_subscript should
> probe for nb_index before giving up. The generic code in
> PyObject_GetItem should also check for nb_index before giving up.
> 

I agree.  These should also be changed. I'll change the PEP, too.
> 
> I think all sequence objects that implement mp_subscript should
> probably be modified according to the lines I sketched above.
>

True.

> 
> This is very close to acceptance. I think I'd like to see the patch
> developed and submitted to SF (and assigned to me) prior to
> acceptance.
> 

O.K. I'll work on it.

-Travis