Need to add to ord and convert to chr

[David Goodger]

on 2000-11-05 15:42, mchitti at my-deja.com (mchitti at my-deja.com) wrote:
> Trying to teach myself python, would appreciate any help.

This is the place!

> I have a long string of letters (a caesar cipher) which I chop up,
> convert to ord values and stick into a list.  I need to be able to add
> an arbitrary interger to the ord values and then convert back to char.
> This should allow me to brute force the cipher if my logic is good.

The other two replies so far have valid points, but the code has a bug.
Caesar ciphers need to wrap around when you add the offset, so that 'z' + 1
== 'a'.

By the way, your example message doesn't seem to be a valid Caesar cipher.
Should it be?

The code below will do what you want, and works in 1.5.2.

-- 
David Goodger    dgoodger at bigfoot.com    Open-source projects:
 - The Go Tools Project: http://gotools.sourceforge.net
 (more to come!)

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#!/usr/bin/env python

import string

def caesar(message, offset):
    result = []
    orda = ord('a')
    ordz = ord('z')
    for c in string.lower(message):
        ordchar = ord(c)
        if orda <= ordchar < ordz:
            result.append(chr((ordchar - orda + offset) % 26 + orda))
        else:                   # if not a letter, don't convert
            result.append(c)
    return string.join(result, '')

message = 'weet bksa myjx oekh fojxed ijktyui!'

for offset in range(26):        # test all offsets
    print '\noffset by:', offset
    result = caesar(message, offset)
    print result