Caesar shift

gistfile1.py

import string

def caesar_shift(s, shift):
    t = string.maketrans(
        string.lowercase + string.uppercase,
        string.lowercase[shift:] + string.lowercase[:shift] + string.uppercase[shift:] + string.uppercase[:shift]
    )
    return s.translate(t)

def rot_13(s):
    return caesar_shift(s, 13)

hi = 'Uryyb, Jbeyq!'
print rot_13(hi)