[Python-ideas] [Python-Dev] Inclusive Range

MRAB python at mrabarnett.plus.com
Tue Oct 5 21:41:46 CEST 2010


On 05/10/2010 20:23, spir wrote:
> On Tue, 05 Oct 2010 13:45:56 +0200
> Boris Borcic<bborcic at gmail.com>  wrote:
>
>> Nick Coghlan wrote:
>>> [...] Being able to say things like
>>> "10:00"<= x<   '12:00", 10.0<= x<   12.0, "a"<= x<   "n" are much
>>> clearer than trying to specify their closed range equivalents.
>>
>> makes one wonder about syntax like :
>>
>> for 10<= x<  20 :
>>       blah(x)
>>
>>
>> Mh, I suppose with rich comparisons special methods, it's possible to turn
>> chained comparisons into range factories without introducing new syntax.
>> Something more like
>>
>>
>> for x in (10<= step(1)<  20) :
>>       blah(x)
>
> About notation, even if loved right-hand-half-open intervals, I would wonder about [a,b] noting it. I guess 99.9% of programmers and novices (even purely amateur) have learnt about intervals at school in math courses. Both notations I know of use [a,b] for closed intervals, while half-open ones are noted either [a,b[ or [a,b). Thus, for me, the present C/python/etc notation is at best misleading.
> So, what about a hypothetical language using directly math *unambiguous* notation, thus also letting programmers chose their preferred semantics (without fooling others)? End of war?
>
Dijkstra came to his conclusion after seeing the results of students
using the programming language Mesa, which does support all 4 forms of
interval.



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