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Changing lowercase characters to uppercase and vice-versa in Python

I'm trying to write a function which given a string returns another string that flips its lowercase characters to uppercase and viceversa.

My current aproach is as follows:

def swap_case(s):
    word = []
    for char in s:
        word.append(char)

    for char in word:
        if char.islower():
            char.upper()
        else:
            char.lower()

    str1 = ''.join(word)

However the string doesn't actually change, how should I alter the characters inside the loop to do so?

PS: I know s.swapcase() would easily solve this, but I want to alter the characters inside the string during a for loop.

Solution 
  • def swap_case(s):
    swapped = []

    for char in s:
        if char.islower():
            swapped.append(char.upper())
        elif char.isupper():
            swapped.append(char.lower())
        else:
            swapped.append(char)

    return ''.join(swapped)