[Tutor] sorting in python

[Python]

On Mon, 2006-06-12 at 11:26 -0400, Kermit Rose wrote:
> #  to insert 3 between 2 and 4 in 
>  
> B = [1,2,4,5]
>  
> B.append(B[3:3])

>>> B[3:3]
[]
>>> B[3:4]
[5]
>>> B[0:1]
[1]
>>> B[:2]
[1, 2]
>>> B.append(B[3:3])
>>> B
[1, 2, 4, 5, []]

>  
> # I expected B[4] to have the value 5 at this point. 
> # It is empty.   Why?

You appended an empty list.  

Note that slice notation returns a list, so you would more commonly use
B.extend(B[0:3]) to avoid nested lists.


The number before the : is the index to include from
The number after the : is the index to exclude

Slices are half-open intervals.  The lower-bound is included while the
upper-bound is excluded.

http://www.cs.utexas.edu/users/EWD/ewd08xx/EWD831.PDF
Provides an excellent justification for this approach
(cited recently on this list)

-- 
Lloyd Kvam
Venix Corp