Caesar, ROT13 encryption/decryption

encryption.py

import collections
import string

def rotate(lst, amount):
  items = collections.deque(lst)
  items.rotate(amount)
  return items

def rotate_str(str, amount):
  return ''.join(rotate(str, amount))

def rotate_str_set(amount):
  from_set = string.ascii_letters
  to_set = rotate_str(string.ascii_lowercase, amount) + \
      rotate_str(string.ascii_uppercase, amount)
  return from_set, to_set

def caes_set():
  return rotate_str_set(-3)

def rot13_set():
  return rotate_str_set(-13)

def caesar_table():
  return string.maketrans(*caes_set())

def reverse_caesar_table():
  return string.maketrans(*caes_set()[::-1])

def rot13_table():
  return string.maketrans(*rot13_set())

def reverse_rot13_table():
  return string.maketrans(*rot13_set()[::-1])

def translate(msg, table):
  return msg.translate(table)

def test(tests, norm, rev):
  for test in tests:
    print translate(test[0], norm) == test[1],\
        translate(test[1], rev) == test[0]
    assert translate(test[0], norm) == test[1] and\
        translate(test[1], rev) == test[0]

if __name__ == '__main__':
  tests_caes = [
      ('TIME WAITS FOR NO MAN', 'WLPH ZDLWV IRU QR PDQ'),
      ('Hello World', 'Khoor Zruog'),
  ]
  tests_rot = [
      ('A good morning to you', 'N tbbq zbeavat gb lbh'),
      ('What is for dinner', 'Jung vf sbe qvaare'),
  ]

  cae_tab = caesar_table()
  rev_cae = reverse_caesar_table()

  rot_tab = rot13_table()
  rev_rot = reverse_rot13_table()

  try:
    test(tests_caes, cae_tab, rev_cae)
    test(tests_rot, rot_tab, rev_rot)
  except AssertionError:
    print 'Test failed!'
  else:
    print 'Tests succeeded.'