[Python-ideas] More useful slices

[Antoine Pitrou]

On Mon, 2 Feb 2015 07:38:52 +1100
Chris Angelico <rosuav at gmail.com> wrote:
> On Mon, Feb 2, 2015 at 5:13 AM, Thomas Kluyver <thomas at kluyver.me.uk> wrote:
> > Iterating over a slice object would work like you were lazily taking that
> > slice from itertools.count() - i.e. iter(a:b:c) would be equivalent to
> > islice(count(), a, b, c). This would also mean that (3:) would have a
> > logical meaning without having to modify range objects to support an
> > optional upper bound. I don't see any logical way to iterate over a slice
> > defined with negative numbers (e.g. (-4:)), so presumably iter(-4:) would
> > raise an exception.
> 
> If you're going to start defining things in terms of
> itertools.count(), I'd prefer to first permit a range object to have
> an infinite upper bound, and then define everything in terms of a
> sliced range - range objects already support clean slicing.
> 
> Is there any particular reason for range objects to disallow infinite
> bounds, or is it just that nobody's needed it?

If the platform's Py_ssize_t type is large enough to represente
positive infinites, then you probably could support infinite range
objects.

Regards

Antoine.