[Python-ideas] More useful slices

[Guido van Rossum]

I don't want to have to have a log drawn-out argument over why I don't like
this proposal or PEP 204. For every reason I can bring up there will surely
be someone who strongly disagrees with that reason. But I'm still going to
reject it -- we already have range() and slice(), with their subtle but
irreconcilable differences, and neither of them is important enough to
warrant any more support built into the language.

On Mon, Feb 2, 2015 at 8:11 AM, Chris Barker - NOAA Federal <
chris.barker at noaa.gov> wrote:

> Please go read PEP 204, as Nick suggested. It would be nice if there was
> more Kongo as to why it was rejected, but it was, indeed, rejected.
>
> I also recall a lot of drawn out threads about more compact syntax for a
> for loop over integers, such as making the integer object iterable:
>
> for I in 10:
>     pass
>
> Which were also all rejected.
>
> Unless someone comes up with a compelling argument that something has
> changed, it seems this conversation has been had already.
>
> -Chris
>
>
>
> On Feb 2, 2015, at 7:02 AM, Neil Girdhar <mistersheik at gmail.com> wrote:
>
> But it is meaningful to have a range with an unspecified stop.  That's
> itertools.count.
>
> On Sunday, February 1, 2015 at 12:27:53 PM UTC-5, Steven D'Aprano wrote:
>>
>> On Sun, Feb 01, 2015 at 04:13:32PM +0100, Todd wrote:
>> > Although slices and ranges are used for different things and
>> implemented
>> > differently, conceptually they are similar: they define an integer
>> sequence
>> > with a start, stop, and step size.
>>
>> I'm afraid that you are mistaken. Slices do not necessarily define
>> integer sequences. They are completely arbitrary, and it is up to the
>> object being sliced to interpret what is or isn't valid and what the
>> slice means.
>>
>> py> class K(object):
>> ...     def __getitem__(self, i):
>> ...             print(i)
>> ...
>> py> K()["abc":(2,3,4):{}]
>> slice('abc', (2, 3, 4), {})
>>
>>
>> In addition, the "stop" argument to a slice may be unspecified until
>> it it applied to a specific sequence, while range always requires
>> stop to be defined.
>>
>> py> s = slice(1, None, 2)
>> py> "abcde"[s]
>> 'bd'
>> py> "abcdefghi"[s]
>> 'bdfh'
>>
>> It isn't meaningful to define a range with an unspecified stop, but it
>> is meaningful to do so for slices.
>>
>>
>> In other words, the similarity between slices and ranges is not as close
>> as you think.
>>
>>
>> --
>> Steven
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-- 
--Guido van Rossum (python.org/~guido)
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