slides/caesar-encipher.html

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  14
  15 # Caesar ciphers
  16
  17 * Letter-by-letter enciphering
  18
  19 ---
  20
  21 # The [string module](http://docs.python.org/3.3/library/string.html) is your friend
  22
  23 ```python
  24 import string
  25 string.ascii_letters
  26 string.ascii_lowercase
  27 string.ascii_uppercase
  28 string.digits
  29 string.punctuation
  30 ```
  31
  32 ---
  33
  34 # Doctest
  35
  36 * Why document?
  37 * Why test?
  38
  39 ---
  40
  41 # The magic doctest incantation
  42
  43 ```python
  44 if __name__ == "__main__":
  45     import doctest
  46     doctest.testmod()
  47 ```
  48
  49 ---
  50
  51 # Doing all the letters
  52
  53 ## Abysmal
  54
  55 ```python
  56 ciphertext = ''
  57 for i in range(len(plaintext)):
  58     ciphertext += caesar_encipher_letter(plaintext[i], key)
  59 ```
  60
  61 ---
  62
  63 # Doing all the letters
  64
  65 ## (Merely) Bad
  66
  67 ```python
  68 ciphertext = ''
  69 for p in plaintext:
  70     ciphertext += caesar_encipher_letter(p, key)
  71 ```
  72
  73 ---
  74
  75 # Doing all the letters
  76
  77 ## Good (but unPythonic)
  78
  79 ```python
  80 ciphertext = map(lambda p: caesar_encipher_letter(p, key), plaintext)
  81 ```
  82
  83 ---
  84
  85 # Doing all the letters
  86
  87 ## Best
  88
  89 ```python
  90 ciphertext = [caesar_encipher_letter(p, key) for p in plaintext]
  91 ```
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