Get OPC data into Python

OPC Python Example

If you want see it for yourself, we have an example that shows how to read a value of an OPC item in Python and print it out. It is just a few lines of code, and with an OPC Data Access server it looks like this:

import win32com.client

# Instantiate the client object 
client = win32com.client.Dispatch('OpcLabs.EasyOpc.DataAccess.EasyDAClient') 

# Perform the operation
value = client.ReadItemValue('', 'OPCLabs.KitServer.2', 'Demo.Single'))

# Display results
print('value: ', value)

The example connects to Simulation OPC Server, but you can quickly modify it to connect to your OPC server instead. Simply download the product and then open the project. 

You can also connect to OPC Unified Architecture (OPC UA) servers, and the code is just as simple:

import win32com.client

# Instantiate the client object
client = win32com.client.Dispatch('OpcLabs.EasyOpc.UA.EasyUAClient') 

# Perform the operation
value = client.ReadValue('opc.tcp://opcua.demo-this.com:51210/UA/SampleServer', 
   'nsu=http://test.org/UA/Data/;i=10853')

# Display results
print('value: ', value)

Besides "one-shot" operations such as reads and writes, you can also set up subscriptions, and receive data change and even event (Alarms & Conditions) notifications:

import time
import win32com.client

# Instantiate the client object
client = win32com.client.Dispatch('OpcLabs.EasyOpc.UA.EasyUAClient') 
client.PullDataChangeNotificationQueueCapacity = 1000
print('Subscribing...')
client.SubscribeDataChange('opc.tcp://opcua.demo-this.com:51210/UA/SampleServer', 
   'nsu=http://test.org/UA/Data/;i=10853', 1000)

print('Processing data change events for 1 minute...')
endTime = time.time() + 60
while time.time() < endTime:
    eventArgs = client.PullDataChangeNotification(2*1000)
    if eventArgs is not None:
        # Handle the notification event
        print(eventArgs)

OPC UA PubSub

The PubSub variety of OPC UA (as opposed to client-server) uses message-oriented middleware to deliver the data. QuickOPC supports it as well, as shown in the example below.

# Define the PubSub connection we will work with.
subscribeDataSetArguments = win32com.client.Dispatch('OpcLabs.EasyOpc.UA.PubSub.OperationModel.EasyUASubscribeDataSetArguments')
connectionDescriptor = subscribeDataSetArguments.DataSetSubscriptionDescriptor.ConnectionDescriptor
connectionDescriptor.ResourceAddress.ResourceDescriptor.UrlString = 'opc.udp://239.0.0.1'

# Instantiate the subscriber object.
subscriber = win32com.client.Dispatch('OpcLabs.EasyOpc.UA.PubSub.EasyUASubscriber') 
subscriber.PullDataSetMessageQueueCapacity = 1000

subscriber.SubscribeDataSet(subscribeDataSetArguments)

print('Processing dataset message events for 20 seconds...')
endTime = time.time() + 20
while time.time() < endTime:
    eventArgs = subscriber.PullDataSetMessage(2*1000)
    if eventArgs is not None:
        print(eventArgs)

Community Use

We have discovered that QuickOPC is being used by an Open Source project smap-data (smap -- Simple Measurement and Actuation Profile). Nice work!