Swap cases in a string

Question

I'm trying to solve this challenge in hackerrank, which asks to convert all lowercase letters to uppercase letters and vice versa.

I attempt it with the following code:

def swap_case(s):
    length = len(s)
    i=0
    while length:
        if s1[i].isupper():
            s[i].lower()
        elif s[i].islower():
            s[i].upper()
        length-=1
        i+=1
    return s

if __name__ == '__main__':
    s = input()
    result = swap_case(s)
    print(result)

However the string returned is the same as it gets passed into the function. Where is the mistake?

strings are not mutable. `s[i].upper()` returns an uppercase "copy" of `s[i]`, it doesn't modify `s[i]` itself. You need to create a new string object entirely... — Julien, May 19 '17 at 06:49
Like @Julien mentioned, you aren't actually changing the original string. Consider using another variable to hold each new update, and return that new variable instead — philip yoo, May 19 '17 at 06:52
Also, for what its worth, Python already has a builtin function which does this: `str.swapcase()`. — Christian Dean, May 19 '17 at 07:08
Does this answer your question? [Swapping uppercase and lowercase in a string](https://stackoverflow.com/questions/36247173/swapping-uppercase-and-lowercase-in-a-string) — Georgy, Aug 21 '20 at 20:58

Arya McCarthy · Accepted Answer · 2017-05-19T08:20:12.020

2

The built-in str.swapcase already does this.

def swap_case(s):
    return s.swapcase()

edited May 19 '17 at 08:20

answered May 19 '17 at 07:43

Arya McCarthy

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1

Worked swiftly. Thanks. – May 19 '17 at 08:56

score 1 · Answer 2 · answered May 19 '17 at 07:09

As said in comments and othe answers, strings are immutable.

Try following:

s = input("Enter input: ")


def convert(ss):
    # Convert it into list and then change it
    newSS = list(ss)
    for i,c in enumerate(newSS):
        newSS[i] = c.upper() if c.islower() else c.lower()
    # Convert list back to string
    return ''.join(newSS)

print(s)
print(convert(s))

# Or use string build in method
print (s.swapcase())

score 1 · Answer 3 · answered Nov 13 '20 at 08:44

def swap_case(s):
    new = ""
    for i in range(len(s)):
        if str.isupper(s[i]):
            new = new + str.lower(s[i])

        elif str.islower(s[i]):
            new = new + str.upper(s[i])

        else:
            new = new + str(s[i])
        
    return (new)

if __name__ == '__main__':
    s = input()
    result = swap_case(s)
    print(result)

gonczor · Answer 4 · 2017-05-19T08:06:41.117

0

As @Julien stated in comment upper and lower methods return a copy, and do not change the object itself. See this docs.

EDIT @aryamccarthy reminded me of already existing feature for this kind of task in python: swapcase() method. See more here. Note this also returns a copy of the string.

edited May 19 '17 at 08:06

answered May 19 '17 at 06:51

gonczor

3,994
1
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I've upvoted your comment, but unfortunatelly these do not give any reputation. – gonczor May 19 '17 at 06:53
@Julien consider adding an elaborated answer. Comments did not increase rep. – Ander2 May 19 '17 at 06:53
@Julien If your words were meant as an answer to the question, maybe you should post an answer instead of commenting the question. – Frerich Raabe May 19 '17 at 06:57

score 0 · Answer 5 · edited Aug 15 '20 at 09:34

0

Try this

def swap_case(s):
    l =[]
    str1 = ''
    for i in s:
        if i.isupper():

            l.append(i.lower())
        elif i.islower():
            l.append(i.upper())
        else:
            l.append(i)
    return (str1.join(l))
if __name__ == '__main__':
    s = input()
    result = swap_case(s)
    print(result)

edited Aug 15 '20 at 09:34

HK boy

1,398
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answered Feb 07 '20 at 01:20

sooraj ks

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score 0 · Answer 6 · answered Mar 28 '20 at 16:43

0

Python-3 in-built swapcase function.

def swap_case(s):
    return s.swapcase()

if __name__ == '__main__':
    s = input()
    result = swap_case(s)
    print(result)

Input:

"Pythonist 3"

Output:

"pYTHONIST 3"

answered Mar 28 '20 at 16:43

Biman Pal

391
4
9

score 0 · Answer 7 · answered May 20 '20 at 09:20

0

def swap_case(s):
    return s.swapcase()

#or you can use list comprehension 

def swap_case(s):
    new=[ch.lower() if ch.isupper() else ch.upper() for ch in s]
    new=''.join(new)
    return new

if __name__ == '__main__':
    s = input()
    result = swap_case(s)
    print(result)

answered May 20 '20 at 09:20

Md. Rizwan Rabbani

21
2

Welcome to SO! You might take the [Tour](https://stackoverflow.com/tour) and you should (re-)read the help topic [How to Answer](https://stackoverflow.com/help/how-to-answer) to get a feeling on how to contribute. You should always explain your code and your answer, so others can profit from it. "Just code" answers are of very poor quality and might be deleted in the future, what would make your work completely useless. – stackprotector May 20 '20 at 09:33

score 0 · Answer 8 · answered Aug 02 '20 at 08:30

0

def swap_case(s):
    l = list(s)
    for i in range(len(s)):
        if l[i].islower():
            l[i] = l[i].upper()
        else:
            l[i] = l[i].lower()
    k = "".join(map(str,l))
    return k

answered Aug 02 '20 at 08:30

Abhinav Mishra

1

or you can also use return s.swapcase() – Abhinav Mishra Aug 02 '20 at 08:31
2

Please don't post only code as answer, but also provide an explanation what your code does and how it solves the problem of the question. Answers with an explanation are usually more helpful and of better quality, and are more likely to attract upvotes. – Mark Rotteveel Aug 02 '20 at 08:55
2

Welcome to Stack Overflow. Code-only answers are discouraged on Stack Overflow because they don't explain how it solves the problem. Please edit your answer to explain what the code does and how it answers the question, so that it is also useful for other users with similar a problem, as well as the OP – Greenonline Aug 02 '20 at 08:56

RISHABH CHATURVEDI · Answer 9 · 2020-08-15T04:51:23.577

0

def swap_case(s):
    a=" "
    for i in s:
        if i==i.lower():
            a=a+(i.upper())
        else:
            a=a+(i.lower())
    return (a)

edited Aug 15 '20 at 04:51

answered Aug 15 '20 at 04:21

RISHABH CHATURVEDI

1
2

score 0 · Answer 10 · answered May 20 '21 at 19:45

import string

upalf = string.ascii_uppercase

lowalf = string.ascii_lowercase

def swap_case(s):
    new = ""
    for i in s:
        if i in upalf:
            new += i.lower()
        elif i in lowalf:
            new += i.upper()
        else:
            new += i
    return new

if __name__ == '__main__':
    s = input()
    result = swap_case(s)
    print(result)

**In this problem, I used the module called "string", inside of it there are attributes that have the Uppercase letter, and lowercase letters **

score -1 · Answer 11 · edited Jan 17 '21 at 17:27

-1

def swap_case(s):
    list_s= list(s)
    for index,char in enumerate(list_s):
        if char == char.lower():
            list_s[index] =char.upper()
        else:
            list_s[index]= char.lower()
            s = ''.join(list_s)
    return s

string = 'HackerRank.com presents "Pythonist 2".'
print(swap_case(string))

edited Jan 17 '21 at 17:27

Ruli

2,592
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answered Jan 17 '21 at 16:55

9 Rules

9
2

It is always better to add a description to the code you post on Stack overflow. – Ruli Jan 17 '21 at 17:28

Swap cases in a string

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