def decipher(self,string):
string = self.remove_punctuation(string)<EOL>ret = '<STR_LIT>'<EOL>for (i,c) in enumerate(string):<EOL><INDENT>if i<len(self.key): offset = self.a2i(self.key[i])<EOL>else: offset = self.a2i(ret[i-len(self.key)])             <EOL>ret += self.i2a(self.a2i(c)-offset)<EOL><DEDENT>return ret<EOL>
Decipher string using Autokey cipher according to initialised key. Punctuation and whitespace
        are removed from the input.       

        Example::

            plaintext = Autokey('HELLO').decipher(ciphertext)     

        :param string: The string to decipher.
        :returns: The enciphered string.