The swapcase function takes a string as an argument, then makes a list of it's characters, loops through them and if a character is a digit it will just skip the iteration, but if it's a letter and it's lowercase then it saves it as uppercase and if it's uppercase then it saves it as lowercase. And the end it joins the list into a string and ret…

swapcase.py

def swapcase(string: str):
    chars = list(string)
    i = 0
    for x in chars:
        if x.isdigit():
            continue
        if x.islower():
            chars[i] = x.upper()
        else:
            chars[i] = x.lower()
        i += 1
    return "".join(chars)

print(swapcase("PythoN"))

Pretty simple.