atbash.py

#!/usr/bin/env python
# -*- coding: utf-8 -*- 
"""atbash.py
"""
from string import letters

def atbash(txt):
    sub_table = zip(letters[:26], "".join(reversed(letters[:26])))
    sub_table += zip(letters[26:], "".join(reversed(letters[26:])))
    sub_table = dict(sub_table)
    s = ""
    for char in txt:
        if char in letters:
            s += sub_table[char]
        else:
            s += char
    return s


print atbash('zfhgrmltroerv@tnzro.xln')