cipher.py

   1 import string
   2 from language_models import *
   3
   4 def caesar_encipher_letter(accented_letter, shift):
   5     """Encipher a letter, given a shift amount
   6
   7     >>> caesar_encipher_letter('a', 1)
   8     'b'
   9     >>> caesar_encipher_letter('a', 2)
  10     'c'
  11     >>> caesar_encipher_letter('b', 2)
  12     'd'
  13     >>> caesar_encipher_letter('x', 2)
  14     'z'
  15     >>> caesar_encipher_letter('y', 2)
  16     'a'
  17     >>> caesar_encipher_letter('z', 2)
  18     'b'
  19     >>> caesar_encipher_letter('z', -1)
  20     'y'
  21     >>> caesar_encipher_letter('a', -1)
  22     'z'
  23     >>> caesar_encipher_letter('A', 1)
  24     'B'
  25     >>> caesar_encipher_letter('é', 1)
  26     'f'
  27     """
  28     letter = unaccent(accented_letter)
  29     if letter in string.ascii_letters:
  30         if letter in string.ascii_uppercase:
  31             alphabet_start = ord('A')
  32         else:
  33             alphabet_start = ord('a')
  34         return chr(((ord(letter) - alphabet_start + shift) % 26) +
  35                    alphabet_start)
  36     else:
  37         return letter
  38
  39 def caesar_decipher_letter(letter, shift):
  40     """Decipher a letter, given a shift amount
  41
  42     >>> caesar_decipher_letter('b', 1)
  43     'a'
  44     >>> caesar_decipher_letter('b', 2)
  45     'z'
  46     """
  47     return caesar_encipher_letter(letter, -shift)
  48
  49 def caesar_encipher(message, shift):
  50     """Encipher a message with the Caesar cipher of given shift
  51
  52     >>> caesar_encipher('abc', 1)
  53     'bcd'
  54     >>> caesar_encipher('abc', 2)
  55     'cde'
  56     >>> caesar_encipher('abcxyz', 2)
  57     'cdezab'
  58     >>> caesar_encipher('ab cx yz', 2)
  59     'cd ez ab'
  60     >>> caesar_encipher('Héllo World!', 2)
  61     'Jgnnq Yqtnf!'
  62     """
  63     enciphered = [caesar_encipher_letter(l, shift) for l in message]
  64     return ''.join(enciphered)
  65
  66 def caesar_decipher(message, shift):
  67     """Decipher a message with the Caesar cipher of given shift
  68
  69     >>> caesar_decipher('bcd', 1)
  70     'abc'
  71     >>> caesar_decipher('cde', 2)
  72     'abc'
  73     >>> caesar_decipher('cd ez ab', 2)
  74     'ab cx yz'
  75     >>> caesar_decipher('Jgnnq Yqtnf!', 2)
  76     'Hello World!'
  77     """
  78     return caesar_encipher(message, -shift)
  79
  80
  81 if __name__ == "__main__":
  82     import doctest
  83     doctest.testmod()