Slicing List or String Object in Python

Question

What is the default range in slicing: For example:

ls = [1, 2, 3, 4, 5]
ls[-3::1]  #returns copy of the elements at indexes -3, -2, -1
ls[-3::-1] #returns copy of the elements at indexes -3 till the start of the list i.e ls[-5]
ls[::-1]   #returns copy of the reverse version of the list
ls[::1]    #return the list as is

What is the idea behind that? How does python determine unstated start and end indexes?

If you have a positive step, then the default start is the start and the default end is the end. If you have a negative step then the default start is the end and the default end is the start. The default step is 1. — khelwood, Jul 18 '20 at 14:09
It's great that you decided to ask community, but this information you can easily find in official docs. So, what's the point? — Olvin Roght, Jul 18 '20 at 14:13
https://stackoverflow.com/questions/509211/understanding-slice-notation — prax, Jul 18 '20 at 14:13

score 1 · Answer 1 · answered Jul 18 '20 at 14:12

If you have a positive step, then the default start is the start and the default end is the end.

If you have a negative step then the default start is the end and the default end is the start.

The default step is 1. The step cannot be zero.

I think that covers all the possibilities.

score 0 · Answer 2 · answered Jul 18 '20 at 14:11

0

For example [a:b:c], so a is start index, b is end index and c means step between indices

answered Jul 18 '20 at 14:11

Krystian

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Slicing List or String Object in Python

2 Answers2