def decipher(self,string):
string = self.remove_punctuation(string)<EOL>ret = '<STR_LIT>'<EOL>for i in range(<NUM_LIT:0>,len(string),<NUM_LIT:2>):<EOL><INDENT>ret += self.decipher_pair(string[i:i+<NUM_LIT:2>])<EOL><DEDENT>return ret<EOL>
Decipher string using Polybius square cipher according to initialised key.

        Example::

            plaintext = Polybius('APCZWRLFBDKOTYUQGENHXMIVS',5,'MKSBU').decipher(ciphertext)     

        :param string: The string to decipher.
        :returns: The deciphered string. The plaintext will be half the length of the ciphertext.