How to use the asyncua.ua.StatusCode function in asyncua

def _create_events_monitored_item(self, params: ua.MonitoredItemCreateRequest):
        self.logger.info("request to subscribe to events for node %s and attribute %s", params.ItemToMonitor.NodeId,
                         params.ItemToMonitor.AttributeId)

        result, mdata = self._make_monitored_item_common(params)
        ev_notify_byte = self.aspace.read_attribute_value(params.ItemToMonitor.NodeId,
                                                          ua.AttributeIds.EventNotifier).Value.Value

        if ev_notify_byte is None or not ua.ua_binary.test_bit(ev_notify_byte, ua.EventNotifier.SubscribeToEvents):
            result.StatusCode = ua.StatusCode(ua.StatusCodes.BadServiceUnsupported)
            return result
        # result.FilterResult = ua.EventFilterResult()  # spec says we can ignore if not error
        mdata.where_clause_evaluator = WhereClauseEvaluator(self.logger, self.aspace, mdata.filter.WhereClause)
        self._commit_monitored_item(result, mdata)
        if params.ItemToMonitor.NodeId not in self._monitored_events:
            self._monitored_events[params.ItemToMonitor.NodeId] = []
        self._monitored_events[params.ItemToMonitor.NodeId].append(result.MonitoredItemId)
        return result

async def write_attribute_value(self, nodeid, attr, value):
        # self.logger.debug("set attr val: %s %s %s", nodeid, attr, value)
        node = self._nodes.get(nodeid, None)
        if node is None:
            return ua.StatusCode(ua.StatusCodes.BadNodeIdUnknown)
        attval = node.attributes.get(attr, None)
        if attval is None:
            return ua.StatusCode(ua.StatusCodes.BadAttributeIdInvalid)

        old = attval.value
        attval.value = value
        cbs = []
        if old.Value != value.Value:  # only send call callback when a value change has happend
            cbs = list(attval.datachange_callbacks.items())

        for k, v in cbs:
            try:
                await v(k, value)
            except Exception as ex:
                self.logger.exception("Error calling datachange callback %s, %s, %s", k, v, ex)

def _add_unique_reference(self, nodedata, desc):
        for r in nodedata.references:
            if r.ReferenceTypeId == desc.ReferenceTypeId and r.NodeId == desc.NodeId:
                if r.IsForward != desc.IsForward:
                    self.logger.error("Cannot add conflicting reference %s ", str(desc))
                    return ua.StatusCode(ua.StatusCodes.BadReferenceNotAllowed)
                break  # ref already exists
        else:
            nodedata.references.append(desc)
        return ua.StatusCode()

def activate_session(self, params, peer_certificate):
        self.logger.info('activate session')
        result = ua.ActivateSessionResult()
        if self.state != SessionState.Created:
            raise ServiceError(ua.StatusCodes.BadSessionIdInvalid)
        if InternalSession._current_connections >= InternalSession.max_connections:
            raise ServiceError(ua.StatusCodes.BadMaxConnectionsReached)
        self.nonce = create_nonce(32)
        result.ServerNonce = self.nonce
        for _ in params.ClientSoftwareCertificates:
            result.Results.append(ua.StatusCode())
        self.state = SessionState.Activated
        InternalSession._current_connections += 1
        id_token = params.UserIdentityToken
        if self.iserver.user_manager is not None:
            if isinstance(id_token, ua.UserNameIdentityToken):
                username = id_token.UserName
                password = id_token.Password
            else:
                username, password = None, None

            user = self.iserver.user_manager.get_user(self.iserver, username=username, password=password,
                                                      certificate=peer_certificate)
            if user is None:
                raise ServiceError(ua.StatusCodes.BadUserAccessDenied)
            else:
                self.user = user

elif vtype == ua.VariantType.XmlElement:
        val = ua.XmlElement(string)
    elif vtype == ua.VariantType.String:
        val = string
    elif vtype == ua.VariantType.ByteString:
        val = string.encode()
    elif vtype in (ua.VariantType.NodeId, ua.VariantType.ExpandedNodeId):
        val = ua.NodeId.from_string(string)
    elif vtype == ua.VariantType.QualifiedName:
        val = ua.QualifiedName.from_string(string)
    elif vtype == ua.VariantType.DateTime:
        val = parser.parse(string)
    elif vtype == ua.VariantType.LocalizedText:
        val = ua.LocalizedText.from_string(string)
    elif vtype == ua.VariantType.StatusCode:
        val = ua.StatusCode(string)
    elif vtype == ua.VariantType.Guid:
        val = uuid.UUID(string)
    else:
        # FIXME: Some types are probably missing!
        raise NotImplementedError
    return val

result = ua.AddNodesResult()

        if not user.role == UserRole.Admin:
            result.StatusCode = ua.StatusCode(ua.StatusCodes.BadUserAccessDenied)
            return result

        if item.RequestedNewNodeId.has_null_identifier():
            # If Identifier of requested NodeId is null we generate a new NodeId using
            # the namespace of the nodeid, this is an extention of the spec to allow
            # to requests the server to generate a new nodeid in a specified namespace
            # self.logger.debug("RequestedNewNodeId has null identifier, generating Identifier")
            item.RequestedNewNodeId = self._aspace.generate_nodeid(item.RequestedNewNodeId.NamespaceIndex)
        else:
            if item.RequestedNewNodeId in self._aspace:
                self.logger.warning("AddNodesItem: Requested NodeId %s already exists", item.RequestedNewNodeId)
                result.StatusCode = ua.StatusCode(ua.StatusCodes.BadNodeIdExists)
                return result

        if item.ParentNodeId.is_null():
            # self.logger.info("add_node: while adding node %s, requested parent node is null %s %s",
            # item.RequestedNewNodeId, item.ParentNodeId, item.ParentNodeId.is_null())
            if check:
                result.StatusCode = ua.StatusCode(ua.StatusCodes.BadParentNodeIdInvalid)
                return result

        parentdata = self._aspace.get(item.ParentNodeId)
        if parentdata is None and not item.ParentNodeId.is_null():
            self.logger.info("add_node: while adding node %s, requested parent node %s does not exists",
                             item.RequestedNewNodeId, item.ParentNodeId)
            result.StatusCode = ua.StatusCode(ua.StatusCodes.BadParentNodeIdInvalid)
            return result

nodedata = NodeData(item.RequestedNewNodeId)

        self._add_node_attributes(nodedata, item, add_timestamps=check)

        # now add our node to db
        self._aspace[nodedata.nodeid] = nodedata

        if parentdata is not None:
            self._add_ref_from_parent(nodedata, item, parentdata)
            self._add_ref_to_parent(nodedata, item, parentdata)

        # add type definition
        if item.TypeDefinition != ua.NodeId():
            self._add_type_definition(nodedata, item)

        result.StatusCode = ua.StatusCode()
        result.AddedNodeId = nodedata.nodeid

        return result

def read_attribute_value(self, nodeid, attr):
        # self.logger.debug("get attr val: %s %s", nodeid, attr)
        if nodeid not in self._nodes:
            dv = ua.DataValue()
            dv.StatusCode = ua.StatusCode(ua.StatusCodes.BadNodeIdUnknown)
            return dv
        node = self._nodes[nodeid]
        if attr not in node.attributes:
            dv = ua.DataValue()
            dv.StatusCode = ua.StatusCode(ua.StatusCodes.BadAttributeIdInvalid)
            return dv
        attval = node.attributes[attr]
        if attval.value_callback:
            return attval.value_callback()
        return attval.value