[Python-ideas] 0-base and 1-base indexed iterables? Custom slicing rules?

[Joonas Liik]

Hey

In one of my projects I'm stuck in an environment where there are multiple
co-existing coding environments, one of which has a convention of using 0
based indexing and the other using 1 based indexing. All i can say is that
is is a VERY (i cant possibly emphasize this enough) bad idea. it is an
unending source of confusion and off by 1 bugs.

It is like the line endings issue all over again ... CR or LF and then you
end up with CR, LF and CR LF, choosing 1 is definitely better than choosing
both. Python got this right, please do not inflict this upon the python
community!

I got real life experience with this and i'm telling you this is a disaster
waiting to happen, please don't..


On 22 March 2015 at 09:24, Luciano Ramalho <luciano at ramalho.org> wrote:

> On Sun, Mar 22, 2015 at 3:38 AM, pedro santos <probiner at gmail.com> wrote:
> > Why can't both 0-base and 1-base indexing exist in the same language,
> and why can't slicing be customized?
>
> Pedro,
>
> The best answer ever is by one of the most important computer
> scientists of the 20th century, Edsger W. Dijkstra -- who was also
> Dutch, like Guido van Rossum:
>
> https://www.cs.utexas.edu/users/EWD/ewd08xx/EWD831.PDF
>
> The answer is also visually beautiful, as are all Dijkstra's
> manuscripts. Some font designer should create a font based on
> Dijkstra's handwriting.
>
> Cheers,
>
> Luciano
>
>
> >
> >
> >
> > If I'm indexing the ruler marks, intervals, boundaries, dots, makes
> sense to start of at 0; rul=[0,1,2,3,4,5,6] would index every mark on my
> ruler so that accordingly rul[0]=0, rul[5]=5.
> > If I'm indexing the blue circles, natural number quantities, objects,
> spans, makes sense to start at 1; cir= [1,2,3,4,5] so that cir[1]=1 and
> cir[5]=5.
> >
> > Now, a lot of the discussion was to do with slicing coupled with the
> indexing and I don't totally understand why.
> >
> > a ≤ x < b is not so intuitive when dealing with objects ("I want balls 1
> up to the the one before 3"), so on one side, you put the finger on what
> you want and on the other, on what you don't want. But this method does
> have the neat property of producing neighbor selections that border
> perfectly, as in [:a][a:b][b:c]. Although in inverse order(-1), the results
> can be unexpected as it returns values off-by-one from its counterpart
> like; L=[0,1,2,3,4,5] so that L[1:3]=[1,2] and L[3:1:-1]=[3:2]. So it's
> consistent with the rule a ≤ x < b, grabbing the lower limit item, but it
> can feel strange by not producing the same selection with inverse order.
> >
> > a ≤ x ≤ b is a natural way to select objets ("I want the balls 1 up to
> 3"), so you're putting the finger on the things you want. If you inverse
> the order(-1) it's still very easy to grasp what are you picking because
> whatever you select it's included like: L=[0,1,2,3,4,5] so that
> L[1:3]=[1,2,3] and L[3:1:-1]=[3,2,1]. Problems seem to arrive though, when
> trying to do neighbor selections, where one would have to do
> [:a][a+1:b][b+1:c] to have the border perfectly. That terrible?
> >
> > Even though one could see a ≤ x < b to be more adept to 0-base, and a ≤
> x ≤ b to be more adept to 1-base, the way I see it, index base and slicing
> rules could be somehow independent. And one would index and slice the way
> it would fit the rationale of the problem or the data, because even slicing
> a 1-base indexed array with a ≤ x < b, would still produce an expected
> outcome, as in cir=[1,2,3,4,5] so that cir[1:3]=[1,2] or cir[:3]=[1,2].
> > Same thing applying a ≤ x ≤ b to a 0-base indexed array, as in
> rul[0,1,2,3,4,5] so that rul[:2]=[0,1,2] or rul[0:2]=[0,1,2].
> >
> > Given that python is an example of human friendly code language,
> emphasizing readability, wouldn't having 0 and 1 base indexing and custom
> slicing methods, improve the thought process when writing and reading the
> code, by fitting them better to specific contexts or data?
> > Is there some language that provides both or each language picks only
> one?
> >
> > Cheers
> >
> >
> > --
> > ________________________________
> >
> > Pedro Alpiarça dos Santos
> > Animator  3DModeler  Illustrator
> > >>  http://probiner.x10.mx/
> >
> >
> > _______________________________________________
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>
>
>
>
> --
> Luciano Ramalho
> |  Author of Fluent Python (O'Reilly, 2015)
> |     http://shop.oreilly.com/product/0636920032519.do
> |  Professor em: http://python.pro.br
> |  Twitter: @ramalhoorg
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