Python for loop: index out of range error

Question

I'm trying to create a loop that will take what the user entered and print it back alternating between upper and lowercase. Ex: the user enters 'helloworld', it prints back 'HeLlOwOrLd'. Here's what I have so far (trust me, I know it's not optimal, it's just what I could get to work):

s = input("enter characters: ")
word = ''
count = 0


for i in s:
        up = s[::2]
        up2 = up.upper()
        up3 = up2[0 + count]
        low = s[1::2]
        low2 = low.lower()
        low3 = low2[0 + count]
        word += up3 + low3
        count += 1

print(word)

When I trace it in the debugger, word comes to the right value, and then it runs the loop again, thus getting the index out of range error. Ideas?

The two most common problems in programming are cache validation, naming things, and off-by-one errors. — TigerhawkT3
– TigerhawkT3, Commented Apr 3, 2015 at 0:25

bucmipid-153 · Accepted Answer · 2015-04-03 00:35:27Z

2

Your looping through too many times. Your splitting s in half in the loop, but looping once for each character in s.

s = input("enter characters: ")
word = ''


for count in range(len(s[::2])):
        up = s[::2]
        up2 = up.upper()
        up3 = up2[0 + count]
        low = s[1::2]
        low2 = low.lower()
        if(len(low2)>count):
            low3 = low2[0 + count]
        else:
            low3=''
        word += up3 + low3
        count += 1

print(word)

Cheers!

answered Apr 3, 2015 at 0:35

bucmipid-153

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2 Comments

tdelaney Over a year ago

Why convert the entire string on each iteration, why do 0 + count and why increment count?

bucmipid-153 Over a year ago

The question asked for help regarding the error. The attempt was to change as little as possible to aide in seeing what caused the error.

TigerhawkT3 · Accepted Answer · 2015-04-03 01:17:18Z

2

count will end up equal to the length of s. However, you are using count as an index for strings that are shorter than s, such as up3.

Try the following:

>>> result = ''
>>> word = 'hello'
>>> for i in range(len(word)):
...     result += (word[i].lower() if i%2 else word[i].upper())
...
>>> result
'HeLlO'

Also:

>>> word = 'HellOWorLD'
>>> ''.join(word[i].lower() if i%2 else word[i].upper() for i in range(len(word)))
'HeLlOwOrLd'

edited Apr 3, 2015 at 1:17

answered Apr 3, 2015 at 0:39

TigerhawkT3

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Comments

tdelaney · Accepted Answer · 2015-04-03 01:04:12Z

0

You could use the case conversion functions from string and itertools.cycle to vary which one is applied to each character. Wrap that all up in a join statement and you get:

''.join(case(c) for case,c in 
    zip(itertools.cycle((string.upper,string.lower)), 'helloworld'))

answered Apr 3, 2015 at 1:04

tdelaney

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