Basic Server Example

Source example: examples/highlevel/basic_server.py

This server creates a small address space with variables and a method below a custom object. It is a compact example of how the high-level server API maps Python code to OPC UA nodes.

Explanation

Building the object tree

The script creates a Plant object below the Objects folder and then adds variables underneath it.

plant = server.add_object("Plant", server.objects_node)

temperature = server.add_variable("Temperature", plant, 22.5, nodeid="ns=1;i=1001")
pressure = server.add_variable("Pressure", plant, 1013.25, nodeid="ns=1;i=1002")
status = server.add_variable("Status", plant, "idle", nodeid="ns=1;i=1003")
counter = server.add_variable("Counter", plant, 0, nodeid="ns=1;i=1004")

Adding a callable method

def add_numbers(a, b):
    return [a + b]

server.add_method(
    "Add",
    plant,
    add_numbers,
    input_args=[
        make_argument("A", "i=11", description="First operand"),
        make_argument("B", "i=11", description="Second operand"),
    ],
    output_args=[
        make_argument("Sum", "i=11", description="A + B"),
    ],
    nodeid="ns=1;i=2001",
)

Updating values at runtime

while True:
    i += 1
    temperature.value = 22.5 + (i % 10) * 0.1
    counter.value = i
    time.sleep(1.0)

Full source

#!/usr/bin/env python3

import time
from o6 import Server
from o6.server import make_argument


def main():
    server = Server(port=4840)

    plant = server.add_object("Plant", server.objects_node)

    temperature = server.add_variable(
        "Temperature",
        plant,
        22.5,
        nodeid="ns=1;i=1001",
    )
    pressure = server.add_variable(
        "Pressure",
        plant,
        1013.25,
        nodeid="ns=1;i=1002",
    )
    status = server.add_variable(
        "Status",
        plant,
        "idle",
        nodeid="ns=1;i=1003",
    )
    counter = server.add_variable(
        "Counter",
        plant,
        0,
        nodeid="ns=1;i=1004",
    )

    def add_numbers(a, b):
        print(f"  Method called: {a} + {b} = {a + b}")
        return [a + b]

    server.add_method(
        "Add",
        plant,
        add_numbers,
        input_args=[
            make_argument("A", "i=11", description="First operand"),
            make_argument("B", "i=11", description="Second operand"),
        ],
        output_args=[
            make_argument("Sum", "i=11", description="A + B"),
        ],
        nodeid="ns=1;i=2001",
    )

    server.start()
    print("Server running at opc.tcp://localhost:4840")
    print("Press Ctrl+C to stop.\n")

    try:
        i = 0
        while True:
            i += 1
            temperature.value = 22.5 + (i % 10) * 0.1
            counter.value = i

            if i % 10 == 0:
                print(f"  Counter={i}, Temp={temperature.value:.1f}")

            time.sleep(1.0)
    except KeyboardInterrupt:
        print("\nShutting down…")
    finally:
        server.stop()
        print("Server stopped.")


if __name__ == "__main__":
    main()