Update the AMP

def update(self, process_list):
        """Update the AMP"""
        # Get the systemctl status
        logger.debug('{}: Update AMP stats using service {}'.format(self.NAME, self.get('service_cmd')))
        try:
            res = self.get('command')
        except OSError as e:
            logger.debug('{}: Error while executing service ({})'.format(self.NAME, e))
        else:
            if res is not None:
                try:
                    msg = u(check_output(res.split(), stderr=STDOUT))
                    self.set_result(to_ascii(msg.rstrip()))
                except CalledProcessError as e:
                    self.set_result(e.output)
            else:
                # Set the default message if command return None
                # Default sum of CPU and MEM for the matching regex
                self.set_result('CPU: {:.1f}% | MEM: {:.1f}%'.format(
                    sum([p['cpu_percent'] for p in process_list]),
                    sum([p['memory_percent'] for p in process_list])))

        return self.result()