def encipher(self,string):
        """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.
        """           
        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
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.