Python - Cipher Problem

[jackboy1608]

Hi,

For Computing GCSE coursework we have to code in Python a Vigenere cipher i have started to do this using code i have sourced from different places on the internet. However i am struggling to make the program work and to make it not bring up any errors.

Any help or tips would be greatly appreciated.

Spoiler

#This is my code

LETTERS = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'

def getMessage():
print('Enter your message:')
return input()

def getKey():
while True:
print('Enter the key number')
return input()

def getMode():
while True:
print('Do you wish to encrypt or decrypt a message?')
mode = input().lower()
if mode in 'encrypt decrypt'.split():
return mode
else:
print('Enter either "encrypt" or "decrypt".')

def main():
# This text can be copy/pasted from http://invpy.com/vigenereCipher.py
myMessage = getMessage()
myKey = getKey()
myMode = getMode()

if myMode == 'encrypt':
translated = encryptMessage(myKey, myMessage)
elif myMode == 'decrypt':
translated = decryptMessage(myKey, myMessage)

print('%sed message:' % (myMode.title()))
print(translated)
print()

def encryptMessage(key, message):
return translateMessage(key, message, 'encrypt')


def decryptMessage(key, message):
return translateMessage(key, message, 'decrypt')


def translateMessage(key, message, mode):
translated = [] # stores the encrypted/decrypted message string

keyIndex = 0
key = key.upper()

for symbol in message: # loop through each character in message
num = LETTERS.find(symbol.upper())
if num != -1: # -1 means symbol.upper() was not found in LETTERS
if mode == 'encrypt':
num += LETTERS.find(key[keyIndex]) # add if encrypting
elif mode == 'decrypt':
num -= LETTERS.find(key[keyIndex]) # subtract if decrypting

num %= len(LETTERS) # handle the potential wrap-around

# add the encrypted/decrypted symbol to the end of translated.
if symbol.isupper():
translated.append(LETTERS[num])
elif symbol.islower():
translated.append(LETTERS[num].lower())

keyIndex += 1 # move to the next letter in the key
if keyIndex == len(key):
keyIndex = 0
else:
# The symbol was not in LETTERS, so add it to translated as is.
translated.append(symbol)

return ''.join(translated)


# If vigenereCipher.py is run (instead of imported as a module) call
# the main() function.
if __name__ == '__main__':
main()