class CesarCipher(object):
    _alphabet = None
    _shift = None

    def set_alphabet(self, value):
        self._alphabet = value

    def set_shift(self, value):
        self._shift = value

    def encode(self, plainText):
        encode_text = ''
        for item in plainText:
            if item not in self._alphabet:
                encode_text += item
            for i in self._alphabet:
                if item == i:
                    index = self.index_of_symbol_in_alphabet(i, self._alphabet)
                    encode_text += self._alphabet[index]

        return encode_text

    def index_of_symbol_in_alphabet(self, symbol, alphabet):
        counter = -1
        for i in alphabet:
            counter += 1
            if alphabet[counter] == symbol:
                index = counter + self._shift
                if index >= len(alphabet):
                    index = index - len(alphabet)
        return index


alphabet = 'abcdefghijklmnopqrstuvwxyz'
plain_text = 'The quick brown fox jumps over the lazy dog'

task = CesarCipher()
task.set_alphabet(alphabet)
task.set_shift(3)
test = task.encode(plain_text)
print(test)