'Modifies an existing high-availability partition group.
:type hapg_arn: string
:param hapg_arn: The ARN of the high-availability partition group to
modify.
:type label: string
:param label: The new label for the high-availability partition group.
:type partition_serial_list: list
:param partition_serial_list: The list of partition serial numbers to
make members of the high-availability partition group.'

def modify_hapg(self, hapg_arn, label=None, partition_serial_list=None):

    params = {'HapgArn': hapg_arn}
    if (label is not None):
        params['Label'] = label
    if (partition_serial_list is not None):
        params['PartitionSerialList'] = partition_serial_list
    return self.make_request(action='ModifyHapg', body=json.dumps(params))
