A ROT13 function for Pyton.

ROT13.py

#By Robin Wellner (gvx)
#I hereby waive copyright and related or neighboring rights to this work
#See the Creative Commons Zero Waiver at <http://creativecommons.org/publicdomain/zero/1.0/>

def rotn(intext, n):
    outtext = []
    for char in intext:
        if 65 <= ord(char) < (65+26):
            char = chr(((ord(char) - 65) +n) % 26 + 65)
        elif 97 <= ord(char) < (97+26):
            char = chr(((ord(char) - 97) +n) % 26 + 97)
        outtext.append(char)
    return ''.join(outtext)

def rot13(intext):
    return rotn(intext, 13)