Negative array indicies and slice()

[Chris Angelico]

On Mon, Oct 29, 2012 at 10:19 PM, Steven D'Aprano
<steve+comp.lang.python at pearwood.info> wrote:
>> In 'C', where Python is written,
>
> That's a popular misapprehension. Python is written in Java, or Lisp, or
> Haskell, or CLR (dot Net), or RPython, or Ocaml, or Parrot. Each of those
> languages have, or had, at least one Python implementation. Oh, there's
> also a version written in C, or so I have heard.

And that's not including the human-brain implementation, perhaps the
most important of all. Although the current port of Python to my brain
isn't quite a complete implementation, lacking a few bits that I
should probably get to at some point, but even so, it's as useful to
me as firing up IDLE.

I wonder if what the OP is looking for is not slicing, but something
more akin to map. Start with a large object and an iterator that
produces keys, and create an iterator/list of their corresponding
values. Something like:

a=[1,2,3,4,5,6,7,8,9,10]
b=[a[i] for i in xrange(-4,3)]

It's not strictly a slice operation, but it's a similar sort of thing,
and it can do the wraparound quite happily.

ChrisA