>>> class Code:
    def __init__(self, code):
        self.code = code
    def encrypt(self):
        self.code = ''.join(chr(ord(char)+1 if ord(char) in (range(65, 90) + range(97, 123)) else ord(char)-25) for char in self.code)
        return self.code
    def decrypt(self):
        self.code = ''.join(chr(ord(char)-1 if ord(char) in (range(65, 90) + range(97, 123)) else ord(char)-25) for char in self.code)
        return self.code

>>> code = Code('MotDePasseSecret')
>>> code.encrypt()
'NpuEfQbttfTfdsfu'
>>> code.decrypt()
'MotDePasseSecret'