inclusive-lower-bound, exclusive-upper-bound (was Re: Range Operation pre-PEP)

[Roman Suzi]

On Fri, 11 May 2001, Andrew Maizels wrote:

> Aahz Maruch wrote:
> > 
> > In article <3AFB0DB9.BDAE54A5 at one.net.au>,
> > Andrew Maizels  <andrew at one.net.au> wrote:
> > >
> > >I can see where consistency is important, but why does Python do the
> > >inclusive-lower-bound, exclusive-upper-bound thing?
> > 
> > Because it makes loops more likely to work.  E.g.:
> > 
> > l = [1,4,9,16]
> > for i in range(len(l)):
> >     print l[i]
> 
> OK, next question: why does Python start indexes at zero?  Your example
> would work perfectly well if the range returned [1, 2, 3, 4] and the
> list was indexed starting with 1.  Basically, range(4) has to produce a
> list of four items, we just differ on what those items should be.
> 
> I'm not just being difficult; I'm trying to design my own language, and
> this is one of the things I have different to Python.  If I've missed
> something where the Python way is superior, then I might want to change
> my mind.
> 
> The way I have things at the moment, in Pixy (my language), array
> indexes default to start at 1, but can be declared to any range (like
> Pascal).  Strings are indexed starting with 1 as well.  Is there a good
> reason not to do this?

That is because numbering starts at point 0 and chars are BETWEEN
points - this way inserts are consistent, because you can specify
any insertion range:

 A B C D E F
0 1 2 3 4 5 6

- so, you can insert something from 1 to 3 ("BC"),
or from 1 to 1 (""):

>>> a = list("ABCDEF")
>>> a[1:3] = list("QQQ")
>>> print a
['A', 'Q', 'Q', 'Q', 'D', 'E', 'F']
>>> a = list("ABCDEF")
>>> a[1:1] = list("QQQ")
>>> print a
['A', 'Q', 'Q', 'Q', 'B', 'C', 'D', 'E', 'F']
>>>

So, this notation is quite convenient, isn't it?

As an exersize, try to do the same with "convenient"
notation:

A B C D E F
1 2 3 4 5 6

or 

A B C D E F
0 1 2 3 4 5
 
> Andrew.

Sincerely yours, Roman A.Suzi
-- 
 - Petrozavodsk - Karelia - Russia - mailto:rnd at onego.ru -