Unrelated to the access path issue, I would like to note that you are not using QuickOPC from Python the way we have documented. It seems that you are somehow referencing the assemblies yourself. But, we have a Python package that does everything for you. Simply install it using 

pip install opclabs_quickopc

and then, in your code, start with

import opclabs_quickopc

# Import .NET namespaces.
from OpcLabs.EasyOpc.DataAccess import *
from OpcLabs.EasyOpc.DataAccess.OperationModel import *


See our Python examples (there are more than 200 of them).

Best regards
 

Hello,
I guess I can still be surprised ( by the access path usage ).

In order to specify the access path, you can create the item descriptor like this:

item_descriptor = DAItemDescriptor(item_id)
item_descriptor.AccessPath = access_path

I hope this helps.
Best regards

I am not actually using the Matrikon OPC Server to subscribe to and read data.  I am trying to connect to one of our local OPC Servers that does require an access path to be used for all data items.  I need to subscribe to, get subscription data and then unsubscribe from the item.

Hello.

If really needed, I can help with properly specifying the access path. However, I seriously doubt that access path is what you are looking for. I am involved with OPC almost from its beginnings, 25-30 years. And in this whole period, I have *never* seen an actual OPC server that would require or even support access paths. Access paths are esoteric feature that only existed in OPC DA specification 1.0, and has been removed in all subsequent versions of the spec.

I suggest that you rather describe what you want to achieve or why you have asked for the access path. I think that with Matrikon OPC server, the ItemID should be sufficient for the server to identify what you want to read, write, or subscribe to.

Best regards

I am looking for some example python code to read an OPC DA item with an access path.  I have installed QuickOPC, python.net, my OPC DA server is running and accessible.  The sample I found looks like this and returns the error: No method matches given arguments for DAItemDescriptor..ctor: (<class 'str'>, <class 'str'>)import clr  # From pythonnet, allows access to .NET assemblies
import sys# Add reference to QuickOPC .NET assembly
# Adjust the path based on where QuickOPC is installed on your systemsys.path.append(r"C:\Program Files (x86)\OPC Labs QuickOPC 2023.2\Assemblies\net472")
clr.AddReference("OpcLabs.EasyOpcClassic")# Import QuickOPC namespaces
from OpcLabs.EasyOpc.DataAccess import EasyDAClient, DAItemDescriptordef read_opc_item():    # Create an instance of the EasyDAClient    client = EasyDAClient()    try:        # Define server, ItemID, and access path        server_name = "Matrikon.OPC.Simulation"  # Replace with your server's ProgID
        item_id = "Random.Int4"                  # Example ItemID (server-specific)
        access_path = "SimulatedData"            # Example access path (server-specific)        # Create a DAItemDescriptor with ItemID and access path
        item_descriptor = DAItemDescriptor(item_id, access_path)        # Read the item from the OPC server
        result = client.ReadItem("", server_name, item_descriptor)        # Check if the read was successful and display the result
        if result.Exception is None:
            print(f"Value: {result.Value}")            print(f"Timestamp: {result.Timestamp}")
            print(f"Quality: {result.Quality}")        else:            print(f"Error reading item: {result.Exception.Message}")
    except Exception as ex:        print(f"An error occurred: {str(ex)}")if __name__ == "__main__":    read_opc_item()