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

[eryksun]

On Fri, Aug 10, 2012 at 6:10 PM, Martin A. Brown <martin at linux-ip.net> wrote:
>
>  : 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))

Close, but you're rotating the lower and uppercase letters together.
In the original they're separate. Here's a different approach using
itertools:

from itertools import islice, cycle
from string import ascii_lowercase, ascii_uppercase

def make_caesar_cipher(alphabet=ascii_lowercase, shift=3):
    return dict(zip(alphabet, islice(cycle(alphabet), shift, None)))

values = make_caesar_cipher()
values.update(make_caesar_cipher(ascii_uppercase))