Problem with changing lowercase letters to uppercase and vice versa using str.replace

Question

Ok, so this is my code, i don't want to use the built in swapcase() method. It does not work for the given string.

def myFunc(a):
    for chars in range(0,len(a)):
        if a[chars].islower():
            a = a.replace(a[chars], a[chars].upper())
        elif a[chars].isupper():
            a = a.replace(a[chars], a[chars].lower())
    return a

print(myFunc("AaAAaaaAAaAa"))

Answer 1

replace changes all the letters and you assign the values back to aso you end up with all upper cases.

def myFunc(a):
    # use a list to collect changed letters
    new_text = []
    for char in a:
        if char.islower():
            new_text.append(char.upper())
        else:
            new_text.append(char.lower())

    # join the letters back into a string
    return ''.join(new_text)

print(myFunc("AaAAaaaAAaAa"))  # aAaaAAAaaAaA

or shorter:

def my2ndFunc(text):
    return ''.join( a.upper() if a.islower() else a.lower() for a in text)

using a list comprehension and a ternary expression to modify the letter (see Does Python have a ternary conditional operator?)