Many people I know ask why Python does slicing the way it does.....
Can anyone /please/ give me a good defense/justification???
I'm referring to why mystring[:4] gives me elements 0, 1, 2 and 3 but *NOT* mystring[4] (5th element).
Many people don't like idea that 5th element is not invited.
(BTW, yes I'm aware of the explanation where slicing is shown to involve slices _between_ elements. This doesn't explain why this is *best* way to do it.)
Chris
Hi Chris,
What I've found is foreword slicing with positive stepping is very convenient for a lot of things. :-)
But when you start trying to use reverse steps, it can get tricky.
There are actually 4 different ways to slice and dice. So we have a pretty good choice. So the trick is to match the slice method to what you need, and also use the correct index's for that method.
Where s = 'abcd' With s[i,j]
Foreword slices index, forward steps
a, b, c, d
i= 0, 1, 2, 3
j= 1, 2, 3, 4s[0,4] = 'abcd' s[1,3] = 'bc'
Foreword slice index (-steps)
a, b, c, d
i= 0, 1, 2, 3
j= -5, -4, -3, -2s[3,-5] = 'dcba' s[2,-4] = 'cb'
Reverse slice index (+steps)
a, b, c, d
i= -4, -3, -2, -1
j= 1, 2, 3, 4s[-4,4] = 'abcd' s[-3,3] = 'bc'
Reverse slice index (-steps)
a, b, c, d
i= -4, -3, -2, -1
j= -5, -4, -3, -2s[-1,-5] = 'dcba' s[-2,-4] = 'cb'
(Maybe this could be made a little more symetrical for Python 3000?)
Cheers, Ron_Adam -- http://mail.python.org/mailman/listinfo/python-list
