AttributeError: 'str' object has no attribute 'write_value'

[Hrathen23]

Hi, Im trying to write with my Client to the Server Struct. I know how to read the struct and how to change each object inside the struct with the opcua-client, but when I try to do it with the python program I can't.

The codes are the minimal server and minimal client changed a bit to do what I need. Here is the server code, in theory its doing what I want:

import asyncio

from asyncua import Server, ua
from asyncua.common.methods import uamethod
from asyncua.common.structures104 import new_struct, new_enum, new_struct_field

@uamethod
def func(parent, value):
    return value * 2


async def main():
    
    server = Server()
    await server.init()
    server.set_endpoint("opc.tcp://localhost:4840/freeopcua/server/") 

    uri = "http://examples.freeopcua.github.io"
    idx = await server.register_namespace(uri)

    myobj = await server.nodes.objects.add_object(idx, "MyObject")
    myvar = await myobj.add_variable(idx, "MyVariable", "")
    
    await server.nodes.objects.add_method(
        ua.NodeId("ServerMethod", idx),
        ua.QualifiedName("ServerMethod", idx),
        func,
        [ua.VariantType.Int64],
        [ua.VariantType.Int64],
    )
    
    snode1, _ = await new_struct(server, idx, "MyStruct", [
        new_struct_field("MyBool", ua.VariantType.String),
        new_struct_field("MyUInt32List", ua.VariantType.String),
    ])
    
    custom_objs = await server.load_data_type_definitions()
    
    mystruct = await server.nodes.objects.add_variable(idx, "my_struct", ua.Variant(ua.MyStruct(), ua.VariantType.ExtensionObject))
    await mystruct.set_writable()
    
    print("Starting server!")
   
    async with server:
        old_struct = await mystruct.get_value()
        old_bool = old_struct.MyBool
        old_uint32_list = old_struct.MyUInt32List
        while True:
            await asyncio.sleep(0.5)
            n_struct = await mystruct.get_value()
            n_bool = n_struct.MyBool
            n_uint32_list = n_struct.MyUInt32List

            if n_bool != old_bool and n_uint32_list != old_uint32_list:

                print("El cliente ha escrito en %s: %s%s" % (mystruct, n_bool,n_uint32_list))
                await mystruct.write_value(n_struct)
                old_bool = n_bool
                old_uint32_list = n_uint32_list
               

try:
    loop = asyncio.get_running_loop()
except RuntimeError:
    loop = None
if loop and loop.is_running():
    print('Async event loop already running. Adding coroutine to the event loop.')
    tsk = loop.create_task(main())
    tsk.add_done_callback(
        lambda t: print(f'Task done with result={t.result()}  << return val of main()'))
else:
    print('Starting new event loop')
    result = asyncio.run(main(), debug=True)

And in the client, I can read each one of the objects inside de structure, but I can't write, I tried to write to the structure, to one of the objects, but nothing.

import asyncio

from asyncua import Client
from asyncua import ua
from asyncua.common.structures104 import new_struct, new_enum, new_struct_field

url = "opc.tcp://localhost:4840/freeopcua/server/"
namespace = "http://examples.freeopcua.github.io"


async def main():

    print(f"Connecting to {url} ...")

    async with Client(url=url) as client:
    
        first_execution = True
        await client.load_data_type_definitions()
 
        while True:
        
            nsidx = await client.get_namespace_index(namespace)
            if first_execution == True:
                print(f"Namespace Index for '{namespace}': {nsidx}")
                first_execution = False
            
            myvar = await client.nodes.root.get_child(
                ["0:Objects", f"{nsidx}:MyObject", f"{nsidx}:MyVariable"]
            )
            
            mystruct = await client.nodes.objects.get_child(f"{nsidx}:my_struct")
            old_struct = await mystruct.get_value()
            old_bool = old_struct.MyBool
            old_uint32_list = old_struct.MyUInt32List
            print(old_bool)
            print(old_uint32_list)



            while True:

                text = str((input("Write something: ")))
                break
                
            await old_bool.write_value(text)

if __name__ == "__main__":
   asyncio.run(main())

To try, the first "version" was the same but only 1 variable and write in that variable and with only this it worked, but now with the structure I don't know what to do.

The error is:

[schroeder-]

You are in the wrong repo. But you can only write the total structure. In your case:

old_struct = await mystruct.get_value()
old_struct.MyBool = 'Text'
await mystruct.write_value(old_struct)

or this way:

val = ua.MyStruct(MyBool='Text')
await mystruct.write_value(val)

[Hrathen23]

Thanks for the help, thats what I wanted to do.