slices - handy summary

[Dustan]

meridian wrote:
> If, like me, you're always forgetting which way around your list/seq
> slices need to go then worry no more. Just put my handy "slice
> lookupper" (TM) ) on a (large!) PostIt beside your screen and, Hey
> Presto! no more tediously typing a 1-9 seq into your interpreter and
> then getting a slice just to check what you get.. (Yes you. You know
> you do that !) ...    Cheers Steve

Actually, I don't. I just remember that, for a natural (positive
nonzero) number y:
x[:y] is the first y elements
x[-y:] is the last y elements

As shown here:
>>> x = range(5)
>>> x
[0, 1, 2, 3, 4]
>>> x[:2]
[0, 1]
>>> x[-2:]
[3, 4]
>>>

And I just work it out from there.

Just my method for remembering slices, that happens to work pretty well
for me.

> x = '0123456789'
>
> x[-10: ] 0123456789 x[  0: ]
> x[ -9: ] 123456789  x[  1: ]
> x[ -8: ] 23456789   x[  2: ]
> x[ -7: ] 3456789    x[  3: ]
> x[ -6: ] 456789     x[  4: ]
> x[ -5: ] 56789      x[  5: ]
> x[ -4: ] 6789       x[  6: ]
> x[ -3: ] 789        x[  7: ]
> x[ -2: ] 89         x[  8: ]
> x[ -1: ] 9          x[  9: ]
>
> x[ :-9 ] 0          x[ :1  ]
> x[ :-8 ] 01         x[ :2  ]
> x[ :-7 ] 012        x[ :3  ]
> x[ :-6 ] 0123       x[ :4  ]
> x[ :-5 ] 01234      x[ :5  ]
> x[ :-4 ] 012345     x[ :6  ]
> x[ :-3 ] 0123456    x[ :7  ]
> x[ :-2 ] 01234567   x[ :8  ]
> x[ :-1 ] 012345678  x[ :9  ]
>          0123456789 x[ :10 ]