CCipher

import math
import string

class CCipher:
    def decode(self, cipherText, shift):
        res = ""
        for val in cipherText:
            res = res + self.getDecodedChar(val, shift)
        return res

    def getDecodedChar(self, char, shift):
        seed = 'AaBbCcDdEeFfGgHhIiJjKkLlMmNnOoPpQqRrSsTtUuVvWwXxYyZz'
        index = seed.find(char)

        if index < 0:
            return char

        res = index - shift*2
        if res < 0:
            res = res + len(seed)
        elif res >= len(seed):
            res = res - len(seed)
        return seed[res]