Python で OPC UA の変数ノードを監視する

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import asyncio
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import random
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from asyncua import Server
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ENDPOINT = 'opc.tcp://localhost:4840'
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NAMESPACE = 'http://examples.freeopcua.github.io'
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async def main() -> None:
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    # Start a server.
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    server = Server()
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    await server.init()
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    server.set_endpoint(ENDPOINT)
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    idx = await server.register_namespace(NAMESPACE)
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    await server.start()
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    print(f'Server started: {server}')
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    # Create a node.
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    myobj = await server.get_objects_node().add_object(idx, 'MyObject')
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    myvar = await myobj.add_variable(idx, 'MyVariable', 1)
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    await myvar.set_writable()
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    # Write a new value every second.
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    while True:
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        await myvar.write_value(random.randint(1, 100))
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        await asyncio.sleep(1)
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if __name__ == '__main__':
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    asyncio.run(main())

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import asyncio
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from asyncua import Client, Node
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from asyncua.common.subscription import DataChangeNotif, SubHandler
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ENDPOINT = 'opc.tcp://localhost:4840'
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NAMESPACE = 'http://examples.freeopcua.github.io'
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class MyHandler(SubHandler):
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    def __init__(self):
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        self._queue = asyncio.Queue()
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    def datachange_notification(self, node: Node, value, data: DataChangeNotif) -> None:
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        self._queue.put_nowait([node, value, data])
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        print(f'Data change notification was received and queued.')
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    async def process(self) -> None:
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        try:
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            while True:
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                # Get data in a queue.
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                [node, value, data] = self._queue.get_nowait()
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                path = await node.get_path(as_string=True)
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                # *** Write your processing code ***
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                print(f'New value {value} of "{path}" was processed.')
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        except asyncio.QueueEmpty:
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            pass
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async def main() -> None:
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    async with Client(url=ENDPOINT) as client:
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        # Get a variable node.
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        idx = await client.get_namespace_index(NAMESPACE)
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        node = await client.get_objects_node().get_child([f'{idx}:MyObject', f'{idx}:MyVariable'])
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        # Subscribe data change.
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        handler = MyHandler()
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        subscription = await client.create_subscription(period=0, handler=handler)
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        await subscription.subscribe_data_change(node)
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        # Process data change every 100ms
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        while True:
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            await handler.process()
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            await asyncio.sleep(0.1)
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if __name__ == '__main__':
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    asyncio.run(main())