Rewrite of the Letterback encrytion script.

Rewritten to make it more modular, basically works the same way as before.

import sys

alphabet = 'abcdefghijklmnopqrstuvwxyz'
balphabet = 'zyxwvutsrqponmlkjihgfedcba'

class LetterBack:
    '''Class for Encrypting a string of letters'''
   
    def __init__(self, text='mnm'):
        self.text = text
       
    def encrypt(self, aSentance):
        '''Encrypts a given string by replacing each letter
        with the letter before it in the alphabet.'''
        output = ''
        for element in aSentance:
            for i in range(26):
                if element == alphabet[i]:
                    output += alphabet[i-1]
        print output

    def decrypt(self, aSentance):
        '''Decrypts a given string encoded by the encrypt
         function.'''
        output = ''
        for element in aSentance:
            #print element + ' this is 1'
            for i in range(26):
                if element == balphabet[i]:
                    output += balphabet[i-1]
        print output

def main():
    lb = LetterBack()
    if sys.argv[1] == '-e':
        lb.encrypt(sys.argv[2])
    elif sys.argv[1] == '-d':
        lb.decrypt(sys.argv[2])

if __name__ == '__main__':
    main()

use:
python letterback.py -e 'alvin'
returns: zkuhm
python letterback.py -d 'zkuhm'
returns: alvin

or in the python interpreter:
>>> from letterback import LetterBack
>>> lb = LetterBack()
>>>lb.encrypt('alvin')
zkuhm
>>> lb.decrypt('zkuhm')
alvin

enjoy :)