documentation

examples/client-subscription.py

@@ -13,28 +13,41 @@ _logger = logging.getLogger('asyncua')
 
 
 class SubscriptionHandler:
+    """
+    The SubscriptionHandler is used to handle the data that is received for the subscription.
+    """
     def datachange_notification(self, node: Node, val, data):
-        """Callback for asyncua Subscription"""
+        """
+        Callback for asyncua Subscription.
+        This method will be called when the Client received a data change message from the Server.
+        """
         _logger.info('datachange_notification %r %s', node, val)
 
 
 async def main():
-    url = 'opc.tcp://localhost:4840/freeopcua/server/'
-    client = Client(url=url)
-    # client.set_security_string()
+    """
+    Main task of this Client-Subscription example.
+    """
+    client = Client(url='opc.tcp://localhost:4840/freeopcua/server/')
     async with client:
-        uri = 'http://examples.freeopcua.github.io'
-        idx = await client.get_namespace_index(uri)
+        idx = await client.get_namespace_index(uri="http://examples.freeopcua.github.io")
         var = await client.nodes.objects.get_child([f"{idx}:MyObject", f"{idx}:MyVariable"])
-
         handler = SubscriptionHandler()
+        # We create a Client Subscription.
         subscription = await client.create_subscription(500, handler)
         nodes = [
             var,
             client.get_node(ua.ObjectIds.Server_ServerStatus_CurrentTime),
         ]
+        # We subscribe to data changes for two nodes (variables).
         await subscription.subscribe_data_change(nodes)
+        # We let the subscription run for ten seconds
         await asyncio.sleep(10)
+        # We delete the subscription (this un-subscribes from the data changes of the two variables).
+        # This is optional since closing the connection will also delete all subscriptions.
+        await subscription.delete()
+        # After one second we exit the Client context manager - this will close the connection.
+        await asyncio.sleep(1)
 
 
 if __name__ == "__main__":