Short rot13 function - Python

It's very simple:

>>> import codecs
>>> codecs.encode('foobar', 'rot_13')
'sbbone'

maketrans()/translate() solutions…

Python 2.x

import string
rot13 = string.maketrans( 
    "ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz", 
    "NOPQRSTUVWXYZnopqrstuvwxyzABCDEFGHIJKLMabcdefghijklm")
string.translate("Hello World!", rot13)
# 'Uryyb Jbeyq!'

Python 3.x

rot13 = str.maketrans(
    'ABCDEFGHIJKLMabcdefghijklmNOPQRSTUVWXYZnopqrstuvwxyz',
    'NOPQRSTUVWXYZnopqrstuvwxyzABCDEFGHIJKLMabcdefghijklm')
'Hello World!'.translate(rot13)
# 'Uryyb Jbeyq!'

This works on Python 2 (but not Python 3):

>>> 'foobar'.encode('rot13')
'sbbone'

The maketrans and translate methods of str are handy for this type of thing.

Here's a general solution:

import string

def make_rot_n(n):
    lc = string.ascii_lowercase
    uc = string.ascii_uppercase
    trans = str.maketrans(lc + uc,
                          lc[n:] + lc[:n] + uc[n:] + uc[:n])
    return lambda s: str.translate(s, trans)

rot13 = make_rot_n(13)

rot13('foobar')
# 'sbbone'