code: def encipher(self,string):
                     
          string = self.remove_punctuation(string)
          ret = ''
          for (i,c) in enumerate(string):
              if i<len(self.key): offset = self.a2i(self.key[i])
              else: offset = self.a2i(string[i-len(self.key)])     
              ret += self.i2a(self.a2i(c)+offset)
          return ret
docs: Encipher string using Autokey cipher according to initialised key. Punctuation and whitespace
          are removed from the input.       
  
          Example::
  
              ciphertext = Autokey('HELLO').encipher(plaintext)     
  
          :param string: The string to encipher.
          :returns: The enciphered string.