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Pure Python OPC-UA client and server library

Project description

OPC UA / IEC 62541 Client and Server for Python >= 3.7 and pypy3 .,

Python package

PyPI Package


opcua-asyncio is an asyncio-based asynchronous OPC UA client and server based on python-opcua, removing support of python < 3.7. Asynchronous programming allows for simpler code (e.g. less need for locks) and potentially performance gains. This library has also sync wrapper over async API which may can be used in sync code instead of python-opcua

OPC UA binary protocol implementation has been tested against many different OPC UA stacks. API offers both a low level interface to send and receive all UA defined structures and high level classes allowing to write a server or a client in a few lines. It is easy to mix high level objects and low level UA calls in one application. Most low level code is autogenerated from xml specification. reports a test coverage of over 95 % of code, most of non-tested code is autogenerated code that is not used yet.


opcua-asyncio is open-source and comes with absolutely no warranty. We try to keep it as much bug-free as possible and try to keep API stable but bugs and API changes will happen! Especially API changes will happen before any 1.0 release.

Some renaming of methods from get_xx to read_xx and set_xx to write_xxx have been made to better follow OPC UA naming conventions

Version 0.9.9 introduces some argument renaming due to more automatic code generation. Especially the arguments to NodeId, BrowseName, LocalizedText and DataValue are now CamelCase instead of lower case, thus follow the OPC Ua convention used in all other structures in this library


With pip

pip install asyncua


We assume that you already have some experience with Python, the asyncio module, the async / await syntax and the concept of asyncio Tasks.

Client class

The Client class provides a high level API for connecting to APU UA servers, session management and access to basic address space services. The client can be used as a context manager. The client will then automatically connect and disconnect withing the withsyntax.

from asyncua import Client

async with Client(url='opc.tcp://localhost:4840/freeopcua/server/') as client:
    while True:
        # Do something with client
        node = client.get_node('i=85')
        value = await node.read_value()

Of course you can also call the connect, disconnect methods yourself if you do not want to use the context manager.

See the example folder and the code for more information on the client API.

Node class

The Node class provides a high level API for management of nodes as well as data access services.

Subscription class

The Subscription class provides a high level API for management of monitored items.

Server class

The Server class provides a high level API for creation of OPC UA server instances.


The documentation is available here ReadTheDocs.

The API remains mostly unchanged in regards to python-opcua. Main difference is that most methods are now async. Please have a look at the examples and/or the code.

A simple GUI client is available:

Browse the examples:

A good starting point are the minimal examples. Minimal client example: Minimal server example:

A set of command line tools also available:

  • uadiscover (find_servers, get_endpoints and find_servers_on_network calls)
  • uals (list children of a node)
  • uahistoryread
  • uaread (read attribute of a node)
  • uawrite (write attribute of a node)
  • uacall (call method of a node)
  • uasubscribe (subscribe to a node and print datachange events)
  • uaclient (connect to server and start python shell)
  • uaserver (starts a demo OPC UA server) tools/uaserver --populate --certificate cert.pem --private_key pk.pem

How to generate certificate:

Client support

What works:

  • connection to server, opening channel, session
  • browsing and reading attributes value
  • getting nodes by path and nodeids
  • creating subscriptions
  • subscribing to items for data change
  • subscribing to events
  • adding nodes
  • method call
  • user and password
  • history read
  • login with certificate
  • communication encryption
  • removing nodes

Tested servers: freeopcua C++, freeopcua Python, prosys, kepware, beckhoff, winCC, B&R, …

Not implemented yet:

  • localized text feature
  • XML protocol
  • UDP (PubSub stuff)
  • WebSocket
  • maybe automatic reconnection...

Server support

What works:

  • creating channel and sessions
  • read/set attributes and browse
  • getting nodes by path and nodeids
  • autogenerate address space from spec
  • adding nodes to address space
  • datachange events
  • events
  • methods
  • basic user implementation (one existing user called admin, which can be disabled, all others are read only)
  • encryption
  • certificate handling
  • removing nodes
  • history support for data change and events
  • more high level solution to create custom structures

Tested clients: freeopcua C++, freeopcua Python, uaexpert, prosys, quickopc

Not yet implemented:

  • UDP (PubSub stuff)
  • WebSocket
  • session restore
  • alarms
  • XML protocol
  • views
  • localized text features
  • better security model with users and password

Running a server on a Raspberry Pi

Setting up the standard address-space from XML is the most time-consuming step of the startup process which may lead to long startup times on less powerful devices like a Raspberry Pi. By passing a path to a cache-file to the server constructor, a shelve holding the address space will be created during the first startup. All following startups will make use of the cache-file which leads to significantly better startup performance (~3.5 vs 125 seconds on a Raspberry Pi Model B).


Code follows PEP8 apart for line lengths which should be max 160 characters and OPC UA structures that keep camel case from XML definition.

All protocol code is under opcua directory

  • asyncua/ua contains all UA structures from specification, most are autogenerated
  • asyncua/common contains high level objects and methods used both in server and client
  • asyncua/client contains client specific code
  • asyncua/server contains server specific code
  • asyncua/utils contains some utilities function and classes
  • asyncua/tools contains code for command lines tools
  • schemas contains the XML and text files from specification and the python scripts used to autogenerate code
  • tests contains tests
  • docs contains files to auto generate documentation from doc strings
  • examples contains many example files
  • examples/sync contains many example files using sync API
  • tools contains python scripts that can be used to run command line tools from repository without installing

Running tests:

python -m pip install -r requirements.txt
python -m pip install -r dev_requirements.txt
pytest -v -s


./ -v -s


pytest -v -s --cov asyncua --cov-report=html


./ -v -s --cov asyncua --cov-report=html

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