[Python-Dev] PEP Proposal: Revised slice objects & lists use slice objects as indexes
Forrest Voight
voights at gmail.com
Mon Mar 10 11:57:30 CET 2008
> I am not sure what you are trying to propose here. The slice object
> isn't special, it's just a regular built-in type.
The idea is to have slice objects be generators. You could make a
slice like 1:10:2 , and that would make a slice object which could be
used as a list index. The list would return a list with the
corresponding item for every index in the generator. Then, lists could
transparently be used as list indexes, or you could supply your own
generator instead of a slice object.
> I don't see how introducing new syntax would simplify indexing.
It would move the slice logic from the list to the slice object. Now
the slice object is just a container, but with this it would be
useful.
> Why should lists accept a list or a generator as an index? What is the
> use case you have in mind?
For example, a multiple selection box's selection would be changed
into its values by supplying the chosen indexes into a list of values.
> > Optionally, the 1:2 syntax would create a slice object outside of list
> > index areas.
>
> Again, I don't see how this could be useful...
> >
> > >>> list(1:5)
> > [1, 2, 3, 4]
> >
> > >>> list(1:5:2)
> > [1, 3]
> >
>
> list(range(1,5,2))?
It would only be useful as shorthand for xrange, but its addition
capabilities would be useful.
> > >>> range(30)[1:5 + 15:17]
> > [1, 2, 3, 4, 15, 16]
> >
>
> This is confusing, IMHO, and doesn't provide any advantage over:
>
> >>> s = list(range(30))
> >>> s[1:5] + s[15:17]
>
I don't think it's confusing. Also, an advantage would be if the slice
object were being automatically generated, this would simplify the
code.
> If you really needed it, you could define a custom class with a fancy
> __getitem__
>
> class A:
> def __getitem__(self, x):
> return x
>
> >>> A()[1:3,2:5]
> (slice(1, 3, None), slice(2, 5, None))
>
> P.S. You should consider using the python-ideas
> (http://mail.python.org/mailman/listinfo/python-ideas) mailing list,
> instead of python-dev for posting suggestions.
>
> Cheers,
> -- Alexandre
>
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