code: def encipher(self,string,keep_punct=False):
          r        
          if not keep_punct: string = self.remove_punctuation(string)
          ret = ''
          for c in string:
              if c.isalpha(): ret += self.i2a( self.a2i(c) + 13 )
              else: ret += c
          return ret
docs: r"""Encipher string using rot13 cipher.
  
          Example::
  
              ciphertext = Rot13().encipher(plaintext)     
  
          :param string: The string to encipher.
          :param keep_punct: if true, punctuation and spacing are retained. If false, it is all removed. Default is False. 
          :returns: The enciphered string.