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A Python library for DLMS/COSEM

Project description

A Python library for DLMS/COSEM.

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pip install dlms-cosem


Full documentation can be found at


dlms-cosem is designed to be a tool with a simple API for working with DLMS/COSEM enabled energy meters. It provides the lowest level function, as protocol state management, APDU encoding/decoding, APDU encryption/decryption.

The library aims to provide a sans-io implementation of the DLMS/COSEM protocol so that the protocol code can be reused with several io-paradigms. As of now we provide a simple client implementation based on blocking I/O. This can be used over either a serial interface with HDLC or over TCP.

We have not implemented full support to be able to build a server (meter) emulator. If this is a use-case you need, consider sponsoring the development and contact us.

Supported features

  • AssociationRequest and AssociationRelease
  • SET
  • DataNotification
  • GlobalCiphering - Authenticated and Encrypted.
  • HLS-GMAC, LLS, HLS-Common auth
  • Selective access via RangeDescriptor
  • Parsing of ProfileGeneric buffers

Example use:

A simple example of reading invocation counters using a public client:

from dlms_cosem.client import DlmsClient
from import TcpTransport, BlockingTcpIO
from import NoSecurityAuthentication
from dlms_cosem import enumerations, cosem

tcp_io = BlockingTcpIO(host="localhost", port=4059)
tcp_transport = TcpTransport(io=tcp_io, server_logical_address=1, client_logical_address=16)
client = DlmsClient(transport=tcp_transport, authentication=NoSecurityAuthentication())
with client.session() as dlms_client:
    data = dlms_client.get(
                             instance=cosem.Obis(0, 0, 0x2B, 1, 0), attribute=2, ))

Look at the different files in the examples folder get a better feel on how to fully use the library.

Supported meters

Technically we aim to support any DLMS enabled meter. The library is implementing all the low level DLMS, and you might need an abstraction layer to support everything in your meter.

DLMS/COSEM specifies many ways of performing tasks on a meter. It is customary that a meter also adheres to a companion standard. In the companion standard it is defined exactly how certain use-cases are to be performed and how data is modeled.

Examples of companion standards are:

  • DSMR (Netherlands)
  • IDIS (all Europe)
  • UNI/TS 11291 (Italy)

On top of it all your DSO (Distribution Service Operator) might have ordered their meters with extra functionality or reduced functionality from one of the companion standards.

We have some meters we have run tests on or know the library is used for in production

  • Pietro Fiorentini RSE 1,2 LA N1. Italian gas meter
  • Iskraemeco AM550. IDIS compliant electricity meter.
  • Itron SL7000
  • Hexing HXF300


The dlms-cosem library is released under the Business Source License 1.1 . It is not a fully Open Source License but will eventually be made available under an Open Source License (Apache License, Version 2.0), as stated in the license document.

Our goal with this licence is to provide enough freedom for you to use and learn from the software without harmful free-riding.

You may make use of the Licensed Work for any Permitted Purpose other than a Competing Use. A Competing Use means use of the Licensed Work in or for a commercial product or service that competes with the Licensed Work or any other product or service we offer using the Licensed Work as of the date we make the Software available.

Competing Uses specifically include using the Licensed Work:

  1. as a substitute for any of our products or services;

  2. in a way that exposes the APIs of the Licensed Work; and

  3. in a product or service that offers the same or substantially similar functionality to the Licensed Work.

Permitted Purposes specifically include using the Software:

  1. for your internal use and access;

  2. for non-commercial education; and

  3. for non-commercial research.

For information about alternative licensing arrangements or questions about permitted use of the library, please contact us at info(at)


This library is developed by Palmlund Wahlgren Innovative Technology AB. We are based in Sweden and are members of the DLMS User Association.

If you find a bug please raise an issue on Github.

We add features depending on our own, and our clients use cases. If you need a feature implemented please contact us.

Training / Consultancy / Commercial Support / Services

We offer consultancy service and training services around this library and general DLMS/COSEM. If you are interested in our services just reach at ìnfo(at)

The library is an important part of our Smart meter platform Utilitarian, If you need to collect data from a lot of DLMS devices or meters, deploying Utilitarian might be the smoothest solution for you.


All notable changes to this project will be documented in this file.

The format is based on Keep a Changelog, and this project adheres to Calendar Versioning








24.1.0 - 2024-01-22


  • Support for HDLC over TCP via composition of IO-implementation separate from transport implementation.
  • Support for LLS (Low Level Security)
  • Support for HLS (method 2) using common method of AES128-ECB.
  • Structlog logging.
  • Implemented VisibleStringData.
  • DlmsConnectionSettings to handle manufacturer specific quirks in communication.


  • Changed License from MIT to BSL v1.1
  • Refactor of authentication to make it simpler support more authentication types. And make it possible to supply manufacturer specific implementations.


  • Shorthand class methods to create DlmsClients. Now composition has to be used.


  • Error in DataArray dlms data type

[21.3.2] - 2021-11-07


Updated dependencies and made it a bit more lenient so installing in other environments will allow for more versions.

[21.3.1] - 2021-06-14


  • To handle the more complicated parsing problem of GET.WITH_LIST with compound data elements a new parser, DlmsDataParser, was added that focuses on only A-XDR DLMS data. Hopefully this can be be used instead of the A-XDR Parser when the parsing of ACSE services APDUs is built away

[21.3.0] - 2021-06-08


  • Added HDLC UnnumberedInformationFrame.
  • Ability to set timeout of transport layer at client level.
  • A simpler way to change client address and invocation counter of a DlmsClient to that reuseing a connection goes smoother
  • Added from_string on Obisthat can parse any viable string as OBIS.
  • Added GET.WITH_LIST service.


  • Renamed classes to exclude Apdu in class names. To have it consistent over the project.
  • Simplified DataNotification
  • Improved handling of pre-established associations
  • Using the wrong data to decrypt now raises DecryptionError instead of InvalidTag
  • The to_string method on Obis now returns in the format 1-8: with a possible override of the separator.


  • Removed the from_dotted, dotted_repr and verbose_repr from Obis


  • Some DLMS over TCP implementations will return partial data. The BlockingTcpTransport now keeps on trying to read the data until all data is received. Fixes #35.
  • Fixed a bug in the HDLC layer that prevented correct sending of segmented information frames.

[21.2.2] - 2021-03-02


  • Fixed missing state management for general ACTION usage

[21.2.1] - 2021-02-18


  • Fixed #23. Typo in A-XDR Parser. Just referenced the function and did not call it. Now DLMS data is interpreted correctly.

  • Fixed #20. It was possible that not calling the .shutdown() on socket before disconnecting made remote modems on meters, that have an embedded TCP/IP stack, keep the socket open and blocking subsequent calls.

[21.2.0] - 2021-01-28


  • Support for basic SET service. No support for WITH_LIST or service specific block transfer

[21.1.2] - 2021-01-22


  • The standard DLMS way of dealing with timezones in datetime are via UTC offset. But the offset is the deviation from normal time to UTC not deviation from UTC. This results in -60 min deviation for UTC+01:00 for example. Previous solution assumed 60 min for UTC+01:00. Solved by negating all values for offset. Note that some DLMS companion standards handles the offset the previous way and in the future there will be need to handle both ways correctly.

  • Included typing-extensions in required packages.

[21.1.1] - 2021-01-13


  • Better handling of TCP errors in BlockingTcpTransport


  • It is now explicitly possible to connect and disconnect a transport in the DlmsClient instead of it being done automatically in .associate() and .release_association(). Context manager .session() works the same.

  • Client to server challenge of DlmsConnection is always created independent of auth method. But only used if needed.


  • Removed conformance validation in DlmsConnection. It seems like meters don't always follow it so better to leave it up to the client.

[21.1.0] - 2021-01-12


  • HDLC transport implementation
  • TCP transport implementation
  • DlMS client implementation
  • Support for Get service including service specific block transfer
  • Support for selective access via range descriptor
  • Support for HLS authentication using HLS-GMAC.
  • Support for GlobalCiphering
  • Parsing of ProfileGeneric buffer


  • Changed project versioning scheme to Calendar versioning



  • UDP messages are now based WrapperProtocolDataUnit to be able to reuse WrapperHeader for TCP messages.
  • Parsing of DLMS APDUs


Initial implementation.

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