Use opcua-asyncio library to create OPC UA service and client, read and write tag values

1. First you need to install Anaconda3
2. Use pip to install opcua-asyncio library

pip install asyncua

3. server.py that can be run directly

import logging
import asyncio
import sys
sys.path.insert(0, "..")

from asyncua import ua, Server
from asyncua.common.methods import uamethod


logging.basicConfig(level=logging.INFO)
_logger = logging.getLogger('asyncua')


@uamethod
def func(parent, value):
    return value * 2


async def main():
    # setup our server
    server = Server()
    await server.init()
    server.set_endpoint('opc.tcp://0.0.0.0:4840/freeopcua/server/')

    # setup our own namespace, not really necessary but should as spec
    uri = 'http://examples.freeopcua.github.io'
    idx = await server.register_namespace(uri)

    # populating our address space
    # server.nodes, contains links to very common nodes like objects and root
    myobj = await server.nodes.objects.add_object(idx, 'MyObject')
    myvar = await myobj.add_variable(idx, 'MyVariable', 6.7)
    # Set MyVariable to be writable by clients
    await myvar.set_writable()
    await server.nodes.objects.add_method(ua.NodeId('ServerMethod', 2), ua.QualifiedName('ServerMethod', 2), func, [ua.VariantType.Int64], [ua.VariantType.Int64])
    _logger.info('Starting server!')
    async with server:
        while True:
            await asyncio.sleep(2)
            new_val = await myvar.get_value() + 0.1
            _logger.info('Set value of %s to %.1f', myvar, new_val)
            await myvar.write_value(new_val)


if __name__ == '__main__':
    asyncio.run(main())

4. Client.py that can be run directly

import asyncio
import sys
# sys.path.insert(0, "..")
import logging
from asyncua import Client, Node, ua

logging.basicConfig(level=logging.INFO)
_logger = logging.getLogger('asyncua')


async def main():
    url = 'opc.tcp://localhost:4840/freeopcua/server/'
    # url = 'opc.tcp://commsvr.com:51234/UA/CAS_UA_Server'
    async with Client(url=url) as client:
        # Client has a few methods to get proxy to UA nodes that should always be in address space such as Root or Objects
        # Node objects have methods to read and write node attributes as well as browse or populate address space
        mytags = await client.nodes.root.get_children()
        #获取根目录下所有node节点
        _logger.info('孩子 of root children are: %r', mytags)
        #获取根目录节点
        _logger.info('孩子 of root are: %r', client.get_root_node())
        mytag1 = await mytags[0].get_children()
        mytag2 = await mytag1[1].get_children()
        #获取指定node下所有node节点,没有返回"[]"
        _logger.info('孩子 of root are: %r',mytag2[0])
        
        uri = 'http://examples.freeopcua.github.io'
        idx = await client.get_namespace_index(uri)
        # get a specific node knowing its node id
        var2 = await client.get_node("i=84").get_children()
        #var2tmp = var2.get_children()
        #_logger.info('Children of root are: %r', var2tmp)
        # var = client.get_node("ns=3;i=2002")
        var = await client.nodes.root.get_child(["0:Objects", f"{idx}:MyObject", f"{idx}:MyVariable"])
        #读取一个node的变量值
        print("My variable", var, await mytag2[0].read_value())
        mytag3 =await mytag2[0].get_children()
        print(var2)
        #写入一个node的变量值
        await mytag2[0].write_value(3.9)
        # print(var)
        # await var.read_data_value() # get value of node as a DataValue object
        # await var.read_value() # get value of node as a python builtin
        # await var.write_value(ua.Variant([23], ua.VariantType.Int64)) #set node value using explicit data type
        # await var.write_value(3.9) # set node value using implicit data type

if __name__ == '__main__':
    asyncio.run(main())