Why Python does *SLICING* the way it does??

[Ron]

Ron wrote:
> seberino at spawar.navy.mil wrote:
> 
>> 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).
>>

 > There are actually 4 different ways to slice ....

> 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,  4
>
> s[0,4] = 'abcd'
> s[1,3] = 'bc'
> .......


Minor correction to this.  It's what I get for not realizing how late it 
was.

Where s = 'abcd'
With s[i:j:step]

Positive slice index, (+1 step)
      a,  b,  c,  d
  i=  0,  1,  2,  3
  j=  1,  2,  3,  4

  s[0:4] = 'abcd'
  s[1:3] = 'bc'

Positive slice index, (-1 step)
      a,  b,  c,  d
  i=  0,  1,  2,  3
  j= -5, -4, -3, -2

  s[3:-5:-1] = 'dcba'
  s[2:-4:-1] = 'cb'

Negative slice index, (+1 step)
      a,  b,  c,  d
  i= -4, -3, -2, -1
  j=  1,  2,  3,  4

  s[-4:4] = 'abcd'
  s[-3:3] = 'bc'

Reverse slice index, (-1 step)
      a,  b,  c,  d
  i= -4, -3, -2, -1
  j= -5, -4, -3, -2

  s[-1:-5:-1] = 'dcba'
  s[-2:-4:-1] = 'cb'



Cheers,
Ron_Adam