number ranges (was Re: Matlab page on scipy wiki)

[Colin J. Williams]

Steven D'Aprano wrote:
> John Zenger wrote:
> 
>> I strongly agree that Python should promote range or xrange to syntax. 
>> I favor [0..10] rather than [0:10] because 0..10 is inherently easier 
>> to understand.
> 
> 
> "Inherently"?
> 
> You mean people are born with an instinctive, unlearnt understanding of 
> ..? Or that our brains are constructed in such a way that .. is easier 
> to understand?
> 
> For what it is worth, even after years of Python programming, I still 
> sometimes write this:
> 
> for i in len(myList):
>     # Oops.
> 
> I too prefer range() or xrange() over magic syntax, but I'm not 
> especially a lover of the range() idiom. How about this? With the 
> introduction of a single keyword, we could do this:
> 
> for i in 2 to 5:
>     print i,
> 
> which would print 2 3 4 5
This could be extended to:
for i in 2 to 5 by 2:
   print i

This would require another reserved word.

Colin W.
> 
> (I'm open to arguments that it should be more Pythonic and less 
> mathematical, and halt at 4.)
> 
> A second keyword "downto" would allow easy backwards loops, and a third 
> "step" will absolutely kill any chance of Guido agreeing to this 
> whatsoever.
> 
> 
> 
>> Haskell also has a good step notation.  In Haskell:
>>
>> [1..10] means [1,2,3,4,5,6,7,8,9,10]
>> [1,3..10] means [1,3,5,7,9]
> 
> 
> I'm wary of that notation. It is too easy to make typos, what with , and 
> . next to each other, and the typos often will not raise an exception 
> but will simply give incorrect but puzzling behaviour. This isn't unique 
> to the proposed syntax (e.g. under Python today it isn't obvious whether 
> [0,3] is a typo for [0.3]) but it gives me pause.
> 
>