number ranges

[Alex Martelli]

Steven D'Aprano <steve at REMOVEMEcyber.com.au> wrote:
   ...
> > Reread the part I quoted above: at least some of the proponents of this
> > syntax appear to be totally ignorant of 30 years of literature and
> > practice of programming, "it will be tough to convince" them that closed
> > intervals are a terrible mistake and semi-open ones the only way to go.
> 
> I intellectually understand that semi-open intervals 
> are the only way to go. But reading the words, the part 
> of my brain that speaks English cries out for a closed 
> interval. Bad brain.

Human brain -- it's harder for non-native-speakers like me to judge the
associations of certain English words in a native speaker's brain.

> Given the overwhelming benefit of semi-closed 
> intervals, I wish to amend my proposal to follow Alex's 
> suggestions, namely:
> 
> for i in (1 to 10 by 3):
>      print i
> 
> should print 1 4 7.

But that would be an "attractive nuisance" to many other native speakers
like you, who would instinctively think of a closed interval.  Maybe
'upto' rather than 'to', as somebody else suggested, would ease that.

> That would make (a to b by c) equivalent to 
> range(a,b,c) except that it returns an iterator rather 
> than a list. Hmmm... putting it that way, the new 
> syntax actually costs 1 keystroke, or saves 1 if you 
> put spaces after the commas in the range expression. 
> Does it add enough clarity and ease of understanding to 
> justify two new keywords?

No, of course not.  And if we use upto, we'll need a downto as well, a
third keyword, for loops with negative step.  range should return an
iterator in Python 3.0 (maybe in 2010?-) and xrange will then go away,
so the only issue is whether syntax sugar for it is SO badly needed as
to justify 2/3 new keywords.

> > whines about it); Python is clearly much better off if such people run
> > away to Ruby, with its (expletive deleted) a..b AND a...b syntaxes just
> > to ensure maximum confusion;-).
> 
> Ruby uses both .. and ...? Now I'm frightened.

I _like_ Ruby, mostly, but yes, it has both a..b AND a...b, one of them
to indicate a semi-open interval and the other to indicate a closed one
(I believe the three dots are for the semi-open, but it could be the
other way 'round) -- I don't remember how it indicates a step. I do
think this is a wart (lack of visual or mnemonic distinction), though
I'm sure Ruby enthusiasts would not agree.


Alex