Proposed PEP: New style indexing, was Re: Bug in slice type

[Raymond Hettinger]

Bryan Olson wrote:
> The conclusion is inescapable: Python's handling of negative
> subscripts is a wart. Indexing from the high end is too useful
> to give up, but it should be specified by the slicing/indexing
> operation, not by the value of the index expression.
>
>
> PPEP (Proposed Python Enhancement Proposal): New-Style Indexing
>
> Instead of:
>
>      sequence[start : stop : step]
>
> new-style slicing uses the syntax:
>
>      sequence[start ; stop ; step]

<klingon>
Bah!
</klingon>

The pythonic way to handle negative slicing is to use reversed().  The
principle is that the mind more easily handles this in two steps,
specifying the range a forward direction, and then reversing it.

IOW, it is easier to identify the included elements and see the
direction of:

     reversed(xrange(1, 20, 2))

than it is for:

     xrange(19, -1, -2)

See PEP 322 for discussion and examples:
   http://www.python.org/peps/pep-0322.html



Raymond