[Tutor] Script won't run for no apparent reason

[Martin A. Brown]

Hello,

 : #!/usr/bin/env python3
 : 
 : import random
 : values = {'a':'d', 'b':'e', 'c':'f', 'd':'g', 'e':'h', 'f':'i', 'g':'j',
 : 'h':'k', 'i':'l', 'j':'m', 'k':'n', 'l':'o', 'm':'p', 'n':'q', 'o':'r',
 : 'p':'s', 'q':'t', 'r':'u', 's':'v', 't':'w', 'u':'x', 'v':'y', 'w':'z',
 : 'x':'a', 'y':'b', 'z':'c', 'A':'D', 'B':'E', 'C':'F', 'D':'G', 'E':'H',
 : 'F':'I', 'G':'J', 'H':'K', 'I':'L', 'J':'M', 'K':'N', 'L':'O', 'M':'P',
 : 'N':'Q', 'O':'R', 'P':'S', 'Q':'T', 'R':'U', 'S':'V', 'T':'W', 'U':'X',
 : 'V':'Y', 'W':'Z', 'X':'A', 'Y':'B', 'Z':'C'}

This sort of thing always catches my eye, and I think to myself....  
'Are there any tools or libraries in this language that I could use 
to generate this, instead of writing out this repetitive data 
structure?'

Here's what I did for my own amusement and possibly of benefit to 
you.  There are probably better solutions out there for your Caesar 
cipher enjoyment, but I hope you may find this helpful.

  # -- This code should create a dictionary that should look like the
  #    one above, but you can create it on the fly with a different
  #    value for the shift.  You could also use a different alphabet.
  #
  def generate_caesar_cipher(alphabet,shift):
      offset = shift - len(alphabet)
      cipheralpha = ''.join((alphabet[offset:], alphabet[0:offset]))
      return dict(zip(alphabet,cipheralpha))
  
  caesar_shift = 3
  
  values = dict()
  values.update(generate_caesar_cipher(string.ascii_letters,caesar_shift))

One other thing to consider is that you can use the underutilized 
function 'translate' from the string module.  The 'maketrans' 
function creates a translation table and the 'translate' function 
applies that to input.

  def alt_trans(plain_alpha,shift):
      offset = shift - len(plain_alpha)
      cipher_alpha = ''.join((plain_alpha[offset:], plain_alpha[0:offset]))
      return string.maketrans(plain_alpha,cipher_alpha)
  
  plaintext = 'Alea iacta est.'
  shift_cipher = alt_trans(string.ascii_letters, caesar_shift)
  ciphertext = string.translate(plaintext,shift_cipher)

Enjoy Python!

-Martin

-- 
Martin A. Brown
http://linux-ip.net/