Discussion on: Daily Challenge #191 - Alphabetical Addition

def add_letter(*letters):
    letters = list(letters)
    start_num = 96
    total = start_num

    if len(letters) == 0:
        letters.append('z')

    for letter in letters:
        letter = str(letter).lower()
        num = ord(letter)

        if num > start_num:
            total += (num - start_num)

        if total > 122:
            total = (total - 122) + start_num

    print 'sum:', chr(total)


# ---------------------

add_letter('a', 'B', 'z')  # = c
add_letter('z', 'a')  # = a
add_letter('a', 'b', 'c')  # = 'f'
add_letter('a', 'b')  # = 'c'
add_letter('z')  # = 'z'
add_letter('z', 'a')  # = 'a'
add_letter('y', 'c', 'b')  # = 'd'
add_letter()  # = 'z'