Rot-13 in Python

rot13.py

#!/usr/bin/env python
from __future__ import print_function
from string import uppercase
key = dict()
for plain,code in zip(uppercase, uppercase[13:]+uppercase[:13]):
    key[plain] = code
    key[plain.lower()] = code.lower()

def rot13(msg):
    results = ''.join([key.get(c,c) for c in msg])
    return results


if __name__ == '__main__':
    import fileinput, sys
    if len(sys.argv) < 2:
        sys.argv.append('-')
    for line in fileinput.input():
        print(rot13(line))