server_example: Read MyVariable using namespace and string identifier

[mahadi]

I am trying to read the "MyVariable" node from server_example .py using (sync) client_example.py.
The examples themselves are working fine, but i ask myself if it shouldnt be possible to read the node also using its name

client.get_node("ns=2;s=MyVariable").read_browse_name()

> BadNodeIdUnknown: "The node id refers to a node that does not exist in the server address space."(BadNodeIdUnknown)

If i recursively traverse the tree i get (the same as UaExpert):

{QualifiedName(NamespaceIndex=2, Name='MyObject'): [
    {QualifiedName(NamespaceIndex=2, Name='MyVariable'): SyncNode(NodeId(Identifier=13, NamespaceIndex=2, NodeIdType=<NodeIdType.FourByte: 1>))},
    ...
]}

And i know from WAGO PLCs that it is possible to read nodes using this method.

Did i miss something here? Or is there a special reason why it doesnt work in the examples?

[AndreasHeine]

looks like ns=2;s=MyVariable does not exist in your ua server!

BadNodeIdUnknown is a response from the server!? maybe the ns-idx wrong?

[mahadi]

It should because in UaExpert, it is visible:

[schroeder-]

NodeId is ns=2;i=13

[schroeder-]

nodeid != browsename try this:
client.get_node("ns=2;i=13")

[mahadi]

Is there a short example somewhere how to do this?

[schroeder-]

myobj = await server.nodes.objects.add_object(NodeId(f'ns={idx};s=MyObject'), "MyObject")
myvar = await myobj.add_variable(NodeId(f'ns={idx};s=MyVariable'), "MyVariable", 6.7)

or

myobj = await server.nodes.objects.add_object(NodeId('MyObject', idx), "MyObject")
myvar = await myobj.add_variable(NodeId('MyVariable', idx), "MyVariable", 6.7)

[mahadi]

Ah great, thanks a lot to both of you for the quick response!

[mahadi]

Btw: For me only the first option worked:

    mynsobj = await server.nodes.objects.add_object(ua.NodeId(f'ns={idx};s=MyObjectNs'), "MyObjectNs")
    mynsvar = await mynsobj.add_variable(ua.NodeId(f'ns={idx};s=MyVariableNs'), "MyVariableNs", 6.1)

For the second one

    mynsobj = await server.nodes.objects.add_object(ua.NodeId(idx, "MyObjectNs"), "MyObjectNs")
    mynsvar = await mynsobj.add_variable(ua.NodeId(idx, "MyVariableNs"), "MyVariableNs", 6.1)

i got:

  File "opcua-asyncio/examples/server-example.py", line 87, in main
    mynsobj = await server.nodes.objects.add_object(ua.NodeId(idx, "MyObjectNs"), "MyObjectNs")
  File "<string>", line 6, in __init__
  File "lib/python3.10/site-packages/asyncua/ua/uatypes.py", line 414, in __post_init__
    elif self.Identifier < 2 ** 16 and self.NamespaceIndex < 255:
TypeError: '<' not supported between instances of 'str' and 'int'

[schroeder-]

My bad wrong argument order:

myobj = await server.nodes.objects.add_object(NodeId('MyObject', idx), "MyObject")
myvar = await myobj.add_variable(NodeId('MyVariable', idx), "MyVariable", 6.7)