def _check_device_number(self, devices):
        '''Check if number of devices is between 2 and 4

        :param kwargs: dict -- keyword args in dict
        '''

        if len(devices) < 2 or len(devices) > 4:
            msg = 'The number of devices to cluster is not supported.'
            raise ClusterNotSupported(msg)
Check if number of devices is between 2 and 4

        :param kwargs: dict -- keyword args in dict