(please create a new forum thread when opening a new issue; you can always hyperlink if there is some relation to other posts)

In your case, you will simply do a "read" on the variable you need. This will be one of the methods like ReadMultipleItems, ReadMultipleItemValues, ReadItem, ReadItemValue.
There are examples for it in the documentation.

Best regards

I am subscribing to several items and would like to occasionally ask for and get the current data from those items.  How would I go about doing that?

Hello.

Sorry, that's because I could not test it right now. Use this instead:



Best regards

# The QuickOPC package is needed. Install it using "pip install opclabs_quickopc".
import opclabs_quickopc
import time

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

# Item changed event handler.
def itemChanged(sender, e):
    if e.Succeeded:
        print(e.Vtq)
    else:
        print('*** Failure: ', e.ErrorMessageBrief, sep='')


# Instantiate the client object.
client = EasyDAClient()

client.ItemChanged += itemChanged

print('Subscribing item changes...')
# IEasyDAClientExtension.SubscribeItem(client, '', 'OPCLabs.KitServer.2', 'Demo.Ramp', 200)
# Define server, ItemID, and access path
server_name = "MyServer.OPC.1" # Replace with your server's ProgID
item_id = "Time2" # Example ItemID (server-specific)
access_path = "Botch" # Example access path (server-specific)

# Create a DAItemDescriptor with ItemID and access path
item_descriptor = DAItemDescriptor(item_id)
item_descriptor.AccessPath = access_path

client.SubscribeItem(ServerDescriptor('', server_name), item_descriptor, DAGroupParameters(200), None)

print('Processing item change notifications for 30 seconds...')
time.sleep(30)

print('Unsubscribing all items...')
client.UnsubscribeAllItems()

client.ItemChanged -= itemChanged

print('Finished.')

Error being returned is:
    client.SubscribeItem(ServerDescriptor('', server_name), item_descriptor, DAGroupParameters(200), None)
AttributeError: 'EasyDAClient' object has no attribute 'SubscribeItem'
 

The basic example for a subscription is here  opclabs.doc-that.com/files/onlinedocs/OPCLabs-OpcStudio/Late...%20to%20a%20single%20item.html and it looks like this (sorry I could not test it at the moment but hopefully it is the right thing):



In this example, replace the line with  by something like the following:



Best regards

I made the changes that you suggested and I'm not sure what's next.  I looked thru the examples and I'm not sure how to subscribe.  Thanks for the assistance.

I was referring to your own code that you posted here.
You have written that you get error on this line:

item_descriptor = DAItemDescriptor(item_id, access_path)     

So I am suggesting to replace this line by the code I have posted, i.e.

item_descriptor = DAItemDescriptor(item_id)
item_descriptor.AccessPath = access_path

Regards

 

I looked thru the python examples, and I am not sure what method to use or how to use the item_descriptor and access path.

Thanks for your patience and assistance.

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