range

[Alex Martelli]

Hilbert wrote:

> Hello,
> 
> Why does range(1,4,1) return [1,2,3]?
> It does not make sense at all.
> It should return [1,2,3,4].
> 
> Am I crazy?

No, just misguided.  The best case I've ever seen made for
always using half-open intervals, i.e., intervals including
the lower bound but NOT including the upper bound, is in Koenig's 
book "C Traps and Pitfalls" -- almost worth learning C to be 
able to follow that exceppent book!-).

Among the many regularities you gain by always using
half-open intervals are, for example, the following two:

len(range(X, Y)) == Y-X                 for any Y>=X
range(A,B)+range(B,C) == range(A,C)     for any A<=B<=C

note the key issue -- the LACK of any need for +1 or -1
in these equalities.  Not having to add or subtract one
means you're far more likely to avoid the frequent bane
of "off-by-one errors".


> Hilbert
> 
> (also 1/2 should return 0.5, but that's another thread)

Sure, but for that you simply need to have a -Qnew on
the python commandline, or a "from __future__ import"
in your source -- it couldn't be done otherwise without
breaking backwards compatibility.  I hope it will be
the default in Python 2.4, but in 2.2 and 2.3 Python
chose to support backwards compatibility instead as
the default -- quite sensibly too, if you think of how
many millions of lines of Python code are in production
programs being used all over the globe.  *With* -Qnew:

[alex at lancelot nubal]$ python -Qnew -c 'print 1/2'
0.5

So there's no particular need for any "other thread"
on this, is there?


Alex