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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def request_pdu(self):
 """ Build request PDU to write single register. :return: Byte array of 5 bytes with PDU. """

        if None in [self.address, self.value]:
            # TODO Raise proper exception.
            raise Exception

        return struct.pack('>BH' + conf.TYPE_CHAR, self.function_code,
                           self.address, self.value)