Untitled

import random
import time
import sys
import os
from string import digits
alphabet = [' ','A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','~','`','!','@','#','$','^','&','*','_','=','/','<','>','?']
def menu_def():
	menu = raw_input("[E]ncode or [D]ecode or [Q]uit:")
	if menu == "e":
		str1 = raw_input("Please enter the string you would like to encode:")
		print "Please enter your secret variable (positive or negative int):"
		secret = 0
		while secret == 0:
			secret = raw_input("")
			if secret == 0:
				print "Please do NOT choose 0 - it will cause problems"
		str1 = str1.lower()
		encoded = []
		for letter in str1:
			int_form = ord(letter) + int(secret)
			str_form = random.choice(alphabet) + str(int_form) + random.choice(alphabet)
			encoded.append(str_form)
		encode_output = ""
		for item in encoded:
			encode_output = encode_output + "," + item
		print "Here is your encoded string:"
		encode_output = encode_output[1:]
		print encode_output
		menu_def()
	elif menu == "d":
		de_output = ""
		print "Please enter the string you would like to decode:"
		str2 = raw_input()
		print "Please enter the secret variable the string was encoded with:"
		secret = 0
		while secret == 0:
			secret = int(raw_input())
			if secret == 0:
				print "The string was not encoded with 0"
		for digit in digits:
			n = int(digit) - secret
			item = chr(int(n))
			de_output = de_output + item
		print de_output
		menu_def()
	elif menu == "q":
		sys.exit(0)
	else:
		print "Invalid Choice!"
		menu_def()
menu_def()