Shift Cipher

shift_2.py

class ShiftCipher:  
    def __init__(self, N = 13):
        [...]
        
    def encrypt_message(self, message):
        encrypted = ""
        #lowercase the message as alphabets are lowercase
        message = message.lower()
        for letter in message:
            if self.original_alphabet.count(letter) > 0:
                #if the letter exists in original alphabet, find the index and add encrypted form
                index = self.original_alphabet.index(letter)
                encrypted += self.cipher_alphabet[index]
            else:
                #if it does not exist in cipher alphabet, do not change the character 
                 encrypted += letter   
        return encrypted

    def decrypt_message(self, message):
        decrypted = ""
        #lowercase the message as alphabets are lowercase
        message = message.lower()
        for letter in message:
            if self.original_alphabet.count(letter) > 0:
                #if the letter exists in original alphabet, find the index and add decrypted form
                index = self.cipher_alphabet.index(letter)
                decrypted += self.original_alphabet[index]
            else:
                #if it does not exist in original alphabet, do not change the character 
                decrypted += letter
        return decrypted