Client Modes Example

Source example: examples/highlevel/client_modes.py

This example shows the different ways the client can be used with and without asyncio.

Explanation

Running inside an async context

The first variant uses async with and awaits the read directly.

asyncio.run(async_client())

Using the client synchronously

The next variant creates a normal client and uses connect, read, and disconnect in sequence.

c = o6.Client()
c.connect()
v = c.read("i=2258")
c.disconnect()

Reusing an event loop

An externally created loop can be passed into the client when loop ownership matters.

loop = asyncio.new_event_loop()
c = o6.Client(loop=loop)

Mixing sync and async calls

The last example mixes both styles. This only works when the loop state matches the operation being performed.

c.connect()
loop.run_until_complete(do_some_async_stuff())
c.disconnect()

Full source

#!/usr/bin/env python3

import sys
import os
import asyncio

sys.path.insert(0, os.path.join(os.path.dirname(__file__), ".."))

import o6
import socket

localhost = socket.gethostname()
endpoint_url = f"opc.tcp://{localhost}:4840"

print("=== Client inside an async context ===")


async def async_client():
    c = o6.Client()
    c.config.endpoint_url = endpoint_url
    async with c:
        v = await c.read("i=2258")
        print(f'Reading value v="{v}"')


asyncio.run(async_client())


print("\n=== Self contained Client (with its own asyncio loop) ===")


def self_contained_client():
    c = o6.Client()
    c.config.endpoint_url = endpoint_url

    c.connect()
    v = c.read("i=2258")
    print(f'Reading value v="{v}"')
    c.disconnect()


self_contained_client()


print("\n=== Reusing event loop outside of async context ===")


def reuse_event_loop_sync():
    loop = asyncio.new_event_loop()

    c = o6.Client(loop=loop)
    c.config.endpoint_url = endpoint_url

    c.connect()
    v = c.read("i=2258")
    print(f'Reading value v="{v}"')
    c.disconnect()


reuse_event_loop_sync()


print("\n=== Reusing event loop inside of async context ===")


def reuse_event_loop_async():
    loop = asyncio.new_event_loop()

    async def main():
        c = o6.Client(loop=loop)
        c.config.endpoint_url = endpoint_url

        async with c:
            future = c.read("ns=1;s=IntegerVariable")
            print("whatever")
            v = await future
            print(f'Reading value v="{v}"')

    loop.run_until_complete(main())


reuse_event_loop_async()


print("\n=== Reusing event loop with mix and match async ===")


def reuse_event_loop_mixmatch():
    loop = asyncio.new_event_loop()
    c = o6.Client(loop=loop)
    c.config.endpoint_url = endpoint_url

    c.connect()

    async def do_some_async_stuff():
        v = await c.read("i=2258")
        print(f'Reading value v="{v}"')

    loop.run_until_complete(do_some_async_stuff())
    c.disconnect()