trigger an even when value changes

[HaythemLtifi]

hello. I am still a noob and i got stuck.
i want the client to read the data only when value changes so i dont kill the net band width.
this is my server code and client code.
the client throw an error. not sure what to do :( .
i want the client to read the speed only when its value changes. hope someone can help me with this.
thanks

code: server
import sys
sys.path.insert(0, "..")
import logging

try:
from IPython import embed
except ImportError:
import code

def embed():
    vars = globals()
    vars.update(locals())
    shell = code.InteractiveConsole(vars)
    shell.interact()

from opcua import ua, Server

logging.basicConfig(level=logging.WARN)
logger = logging.getLogger("opcua.server.internal_subscription")
logger.setLevel(logging.DEBUG)

server = Server()
server.set_endpoint("opc.tcp://localhost:4840/freeopcua/server/")

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

objects = server.get_objects_node()

myobj = objects.add_object(idx, "MyObject")
myvar = myobj.add_variable(idx, "Speed", ua.Variant(0, ua.VariantType.Float))

etype = server.create_custom_event_type(idx, 'MyFirstEvent', ua.ObjectIds.BaseEventType, [('Speed', ua.VariantType.Float)])

myevgen = server.get_event_generator(etype, myobj)

server.start()

try:

import time
count = 0
while True:
    time.sleep(5)
    myevgen.event.Message = ua.LocalizedText("MyFirstEvent %d" % count)
    myevgen.event.Speed = count
    myvar.set_value(count)

    
    myevgen.trigger()
 
    count += 1
    print(count)

embed()

finally:

server.stop()

code client
import sys
sys.path.insert(0, "..")

try:
from IPython import embed
except ImportError:
import code

def embed():
    vars = globals()
    vars.update(locals())
    shell = code.InteractiveConsole(vars)
    shell.interact()

from opcua import Client

class SubHandler(object):

"""
Subscription Handler. To receive events from server for a subscription
data_change and event methods are called directly from receiving thread.
Do not do expensive, slow or network operation there. Create another
thread if you need to do such a thing
"""
def event_notification(self, event):
    speednode=client.get_node("ns=2;i=2")
    speed=speednode.get_value()
    print(speed)

client = Client("opc.tcp://localhost:4840/freeopcua/server/")

try:
client.connect()

root = client.get_root_node()
print("Objects node is: ", root)


obj = root.get_child(["0:Objects", "2:MyObject"])
print("MyObject is: ", obj)

myevent = root.get_child(["0:Types", "0:EventTypes", "0:BaseEventType", "2:MyFirstEvent"])
print("MyFirstEventType is: ", myevent)

msclt = SubHandler()
sub = client.create_subscription(100, msclt)
handle = sub.subscribe_events(obj, myevent)

embed()
sub.unsubscribe(handle)
sub.delete()

finally:
client.disconnect()

[AndreasHeine]

why not subscribing the data itself and always have the latest value (the datachangenotification is report by exception so only if the value changes) and be careful in you subhandler the doc string says do not do slow / network tasks in there ... get_value() is a network call!

[HaythemLtifi]

thanks you i will do that , i will see how to work around the network call.

[HaythemLtifi]

thanks to you i managed to do the use the datachangenotification .
but what if i wanted to get notification from different node values any hints?
code;
import sys
sys.path.insert(0, "..")
from IPython import embed
from opcua import Client
from opcua import ua

class SubHandler(object):

"""
Subscription Handler. To receive events from server for a subscription
data_change and event methods are called directly from receiving thread.
Do not do expensive, slow or network operation there. Create another
thread if you need to do such a thing
"""
def datachange_notification(self, node, val, data):
    print("Python: New data change event", node, val )
    
    timestamp = data.monitored_item.Value.SourceTimestamp

    tag_name = node.nodeid

    print (timestamp, tag_name, val)

client = Client("opc.tcp://localhost:4840/freeopcua/server/")

try:

client.connect()
root = client.get_root_node()
print("Objects node is: ", root)
obj = root.get_child(["0:Objects", "2:MyObject"])
print("MyObject is: ", obj)
handler  = SubHandler()
sub = client.create_subscription(100, handler )
node = client.get_node("ns=2;i=2")
handle2 = sub.subscribe_data_change(client.get_node("ns=2;i=3"))
handle = sub.subscribe_data_change(client.get_node("ns=2;i=2"))
embed()
sub.unsubscribe(handle)
sub.delete()

finally:
client.disconnect()
exit()

[HaythemLtifi]

i found it .
i thought that i will over right the handle but i guess its smarted then me. nice job developers

[Kog008]

In that context, honestly: I dont understand the embed() function. Can someone please explain it? My OPC client is going to run in an exe-file. Is the embed() approach still the way to go for looping infinitely my OPC client?

[scch1092]

is it possible that the "sub.unsubscribe(hanlde)" is not working? After running "sub.unsubscribe(handle)" I still get messages in the output

[AndreasHeine]

i assume your handle is wrong!

[scch1092]

You are right. I found my mistake, subscribing works! Thank you!