[Python-3000] Making more effective use of slice objects in Py3k

[Guido van Rossum]

On 8/26/06, Jim Jewett <jimjjewett at gmail.com> wrote:
> On 8/26/06, Josiah Carlson <jcarlson at uci.edu> wrote:
> > Nick Coghlan <ncoghlan at iinet.net.au> wrote:
>
> > > There are a couple of existing workarounds for
> > > this: buffer() objects, and the start/stop arguments
> > > to a variety of string methods. Neither of these is
> > > particular convenient to work with, and buffer() is
> > > slated to go away in Py3k.
>
> > Ahh, but string views offer a significantly more
> > reasonable mechanism.
>
> As I understand it, Nick is suggesting that slice objects be used as a
> sequence (not just string) view.

I have a hard time parsing this sentence. A slice is an object with
three immutable attributes -- start, stop, step. How does this double
as a string view?

> > string = stringview(string)
> > ...  We can toss all of the optional start, stop
> > arguments to all string functions, and replace them
> > with either of the following:
> >     result = stringview(string, start=None, stop=None).method(args)
>
> >     string = stringview(string)
> >     result = string[start:stop].method(args)
>
> Under Nick's proposal, I believe we could replace it with just the final line.

I still don't see the transformation of clumsy to elegant. Please give
me a complete, specific example instead of a generic code snippet.
(Also, please don't use 'string' as a variable name. There's a module
by that name that I can't get out of my head.)

Maybe the idea is that instead of

  pos = s.find(t, pos)

we would write

  pos += stringview(s)[pos:].find(t)

???

And how is that easier on the eyes? (And note the need to use +=
because the sliced view renumbers the positions in the original
string.)

>     result = string[start:stop].method(args)
>
> though there is a chance that (when you want to avoid copying) he is
> suggesting explicit slice objects such as
>
>     view=slice(start, stop)
>     result = view(string).method(args)

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)