Python string index out of bounds

Question

I want to reverse a string like so:

def reverse(s):
    for i in range(len(s),0,-1):
        var = s[i] # getting an out of range error?
        ...

Can someone explain why?

len(s) == N, s[N] is out of bounds, the last valid index is N-1 — user1514631
– user1514631, Commented Oct 22, 2015 at 9:10
I find reversed(range(len(s))) more readable than range(len(s)-1,-1,-1) — John La Rooy
– John La Rooy, Commented Oct 22, 2015 at 9:19
FYI there is a easier way s[::-1] would also reverse the string. — Pavan Gupta
– Pavan Gupta, Commented Oct 22, 2015 at 9:43

Ziezi · Accepted Answer · 2015-10-22 09:25:04Z

3

If a string length is n, the valid indexes are from 0 to n-1 (the elements are counted from 0 not from 1).

In your code the for loop condition len(s) should be changed into len(s) - 1.

answered Oct 22, 2015 at 9:13

Ziezi

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1 Comment

Thank you for a quick and simple answer! Will accept the answer in 7 minutes.

Remi Guan · Accepted Answer · 2015-10-22 09:18:00Z

1

simplicis's answer is so good, but here is an easy way to reverse a string like this:

print('Hello'[::-1])

Output:

olleH

answered Oct 22, 2015 at 9:18

Remi Guan

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Thanks for the response as well! I'm doing a Codecademy tutorial, and they specifically instructed not to use it that way ;) but I appreciate it!

Okay, just a tip. If you want to reverse a string, this is the best way :P