slides/caesar-encipher.html

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  33
  34 # Caesar ciphers
  35
  36 ![centre-aligned Caesar wheel](caesarwheel1.gif)
  37
  38 * Letter-by-letter enciphering
  39
  40 ---
  41
  42 # The [string module](http://docs.python.org/3.3/library/string.html) is your friend
  43
  44 ```python
  45 import string
  46 string.ascii_letters
  47 string.ascii_lowercase
  48 string.ascii_uppercase
  49 string.digits
  50 string.punctuation
  51 ```
  52
  53 ---
  54
  55 # Doctest
  56
  57 * Why document?
  58 * Why test?
  59
  60 ---
  61
  62 # The magic doctest incantation
  63
  64 ```python
  65 if __name__ == "__main__":
  66     import doctest
  67     doctest.testmod()
  68 ```
  69
  70 ---
  71
  72 # Doing all the letters
  73
  74 ## Abysmal
  75
  76 ```python
  77 ciphertext = ''
  78 for i in range(len(plaintext)):
  79     ciphertext += caesar_encipher_letter(plaintext[i], key)
  80 ```
  81
  82 ---
  83
  84 # Doing all the letters
  85
  86 ## (Merely) Bad
  87
  88 ```python
  89 ciphertext = ''
  90 for p in plaintext:
  91     ciphertext += caesar_encipher_letter(p, key)
  92 ```
  93
  94 ---
  95
  96 # Doing all the letters
  97
  98 ## Good (but unPythonic)
  99
 100 ```python
 101 ciphertext = map(lambda p: caesar_encipher_letter(p, key),
 102                 plaintext)
 103 ```
 104
 105 ---
 106
 107 # Doing all the letters
 108
 109 ## Best
 110
 111 ```python
 112 ciphertext = [caesar_encipher_letter(p, key)
 113                 for p in plaintext]
 114 ```
 115
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