Vigenere Cipher 'string Index Out Of Range' For Decryption

my Vigenere cipher works perfectly for encryption but I just need to fix this problem for decryption where I am told, after running the program, that the string index is out of ran

Solution 1:

If your key text is longer than key phrase you'll get an invalid index here : new = ord(_key_phrase[letters]) - ord(_key_text[letters%len(_key_text)]) when letters becomes greater than len(_key_text)

You have key_text on both places in encryption and key text and key phrase in decryption so you have to change one variable here.