ROT Brute force python script

rot.py

from sys import argv

message = argv[1]
LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
letters = 'abcdefghijklmnopqrstuvwxyz'

for key in range(26):
    translated = ''
    for letter in message:
        if letter.isupper():
            current_alphabet = LETTERS
        else:
            current_alphabet = letters
        num = current_alphabet.find(letter)
        num = num - key
        if num < 0:
            num = num + len(current_alphabet)
        translated += current_alphabet[num]
    print('Key %s: %s' % (key, translated))