Python String Slicing Using Negative Step

Question

I have the following program:

str = 'abcd'
l = len(str)

str2 = str[l-1:0:-1] 

print(str2)

str2 = str[l-1:-1:-1] 

print(str2)

Why does the first print() output dcb and the second print() output an empty string ? Why doesn't the second print() output dcba ?

The numbers you use to split, you can read about it [here](https://stackoverflow.com/a/509295/13781503) — Ethan M-H, Jul 23 '20 at 04:50
We expect you to use available documentation and resources before posting here. — Prune, Jul 23 '20 at 05:13

score 1 · Answer 1 · answered Jul 23 '20 at 04:58

In the statement str[l-1:0:-1] - Last character upto 0th character not including the zeroth element. That's why you get dcb

In the statement str2 = str[l-1:-1:-1] you are going from 3rd index to 3rd index so empty string.

If you need all elements str2 = str[l-1::-1] would give dcba

score 0 · Answer 2 · answered Jul 23 '20 at 04:55

0

First case, l=4. You slice abcd from 3 to 0, resulting in dcb. Second case you slice from 3 to -1. -1 is the last element of the list/string. So you are sliciing from 3 to 3, resulting in nothing.

answered Jul 23 '20 at 04:55

ZWang

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Python String Slicing Using Negative Step

2 Answers2