Connect / disconnect¶

Every client session in o6 starts with constructing a Client and ends with a clean shutdown. This page walks through the four common shapes that construction and connection can take.

This tutorial expects the example server running in the background.

Create a client — basic connect / disconnect¶

A client is constructed with the endpoint URL of the server you want to talk to. When you are done, call disconnect().

from o6 import Client

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

After creation we can connect the client object to the server at the selected endpoint.

client.connect()
print(client.connected)   # True

When we are done with the client we disconnect.

client.disconnect()
print(client.connected)   # False

Putting it all together¶

from o6 import Client

client = Client("opc.tcp://localhost:4840")
client.connect()
print(client.connected)   # True

# ... do some work

client.disconnect()
print(client.connected)   # False

Connect with context manager¶

Client is a context manager, both synchronously and asynchronously. The with / async with block calls connect() on entry and disconnect() on exit, including on exceptions. The with form is the recommended shape for short scripts and one-off scripts.

from o6 import Client

with Client("opc.tcp://localhost:4840") as client:
    print(client.connected)   # True — connected on entry
    # ... do work ...

# disconnected automatically here, even if the body raised

Async: the async with form is covered in Async client.

Create-client options¶

Client.__init__ takes the endpoint URL and an optional loop, plus a number of keyword-only options for authentication, encryption, and bookkeeping. They declare sensible defaults and only need to be set when needed.

name="..." — A label used to identify the client. If you create more than one client in the same process, give each one a distinct name; otherwise o6 assigns one automatically (client1, client2, …). Must be a valid Python identifier, must not match server\d+, and must not be ::global / global.

from o6 import Client
line_a = Client("opc.tcp://line-a:4840", name="simple_client")

logger=... — A logging.Logger for the client to log to. Defaults to a logger named after the module if not set.

import logging
from o6 import Client

log = logging.getLogger("my_app.opc")
client = Client("opc.tcp://localhost:4840", logger=log)

username=..., password=... — Username/password authentication. The server's UserTokenPolicy must allow this; otherwise the activateSession step will fail.

from o6 import Client

client = Client("opc.tcp://localhost:4840", username="alice", password="s3cr3t")