[Tutor] a function I fail to understand

[David]

Hello list,

I am having trouble understanding the following function. What trips me
up is the "letter = letter.lower()" line.

As I understand, the function takes a letter and assigns True to a
letter if it is upper case.

But then he goes to

letter = letter.lower()

and all letters are converted back to lower again!?? The point is that,
to my understanding, the logic follows from the first block to
letter = letter.lower(). Isn't that true?

Thanks for helping me out,

David


def rotate13_letter(letter):
    """
    Return the 13-char rotation of a letter.
    """
    do_upper = False
    if letter.isupper():
        do_upper = True

    letter = letter.lower()
    if letter not in CHAR_MAP:
        return letter

    else:
        letter = CHAR_MAP[letter]
        if do_upper:
            letter = letter.upper()

    return letter