Getting an IndexError: string index out of range

Question

I'm not sure why I'm getting an

IndexError: string index out of range

with this code.

s = 'oobbobobo'
a = 0
for b in range(len(s)-1):
    if (s[b] == 'b') and (s[b+1] == 'o') and (s[b+2] == s[b]):
        a += 1
    elif (s[b] == 'b') and (s[b+1] == 'o') and None:
        break 

print("Number of times bob occurs is: ", a)

I thought the elif statement would fix the error, so I'm lost.

your for loop termination condition is wrong, it should be: for b in range(len(s)-3): — TuanDT
– TuanDT, Commented Sep 8, 2016 at 3:16

mgilson · Accepted Answer · 2016-09-08 03:15:55Z

3

In this case, the length of s is 9 which means that you're looping over range(8) and therefore the highest value that b will have is 7 (Stay with me, I'm going somewhere with this ...)

When b = 7 (on the last iteration of the loop), the conditional expression in the if statement is being checked which contains:

(s[b+2] == s[b])

Well, since b = 7, b + 2 = 9, but s[9] will be out of bounds (remember, python is 0 indexed so the highest index in a a string of length 9 is 8).

I'm guessing that the fix is to just modify the range statement:

for b in range(len(s)-2):
    ...

answered Sep 8, 2016 at 3:15

mgilson

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