KEY = "BOB" def encode_phrase(phrase, key): result = "" k = 0 for i in range(len(phrase)): if phrase[i].isalpha(): result += KEY[k]+ str(findDiff(phrase[i],key[k])) k+= 1 else: result += phrase[i] if k == len(KEY): k = 0 return result def decode_phrase(phase, key): def findDiff(letter1,letter2): diff = ord(letter1) - ord(letter2) if diff < 0: diff += 26 return diff 

How would I make a function that decodes the result that encode_phrase encodes?