def rot(s, n=13):
    r = ""
    for c in s:
        cc = c
        if cc.isalpha():
            cc = cc.lower()
            o = ord(cc)
            ro = (o+n) % 122
            if ro == 0: ro = 122
            if ro < 97: ro += 96
            cc = chr(ro)
        r = ''.join((r,cc))
    return r

This function takes 2 arguments, first is the string to be encoded (or decoded) the second is optional and can be used to change the rotation amount to something other than 13.

Flexible Rot13 Function

python

Python