String manipulation in python..NEED HELP!!!!

[duncan smith]

On 10/12/12 22:38, qbailey at ihets.org wrote:
> I need help with a program i am doing. it is a cryptography program. i am given a regular alphabet and a key. i need to use the user input and use the regular alphabet and use the corresponding letter in the key and that becomes the new letter. i have the basic code but need help with how to mainpulate the string to do the encryption/decryption. please help
>
> here is my code so far:
>
>
> """ crypto.py
>      Implements a simple substitution cypher
> """
>
> alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
> key =   "XPMGTDHLYONZBWEARKJUFSCIQV"
>
> def main():
>    keepGoing = True
>    while keepGoing:
>      response = menu()
>      if response == "1":
>        plain = raw_input("text to be encoded: ")
>        print encode(plain)
>      elif response == "2":
>        coded = raw_input("code to be decyphered: ")
>        print decode(coded)
>      elif response == "0":
>        print "Thanks for doing secret spy stuff with me."
>        keepGoing = False
>      else:
>        print "I don't know what you want to do..."
>
>
>
>
> i really need help on how to encrypt it im not sure how to go about doing that please help.
>

 >>> alpha = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
 >>> key = "XPMGTDHLYONZBWEARKJUFSCIQV"
 >>> mapping = {}
 >>> for i, ch in enumerate(alpha):
	mapping[ch] = key[i]

	
 >>> ''.join(mapping[ch] for ch in "ACE")
'XMT'
 >>> ''.join(mapping[ch] for ch in "WORD")
'CEKG'
 >>>


Duncan