PyModbus - A Python Modbus Stack

image image Documentation Status Downloads


Pymodbus is a full Modbus protocol implementation using twisted for its asynchronous communications core. It can also be used without any third party dependencies (aside from pyserial) if a more lightweight project is needed. Furthermore, it should work fine under any python version > 2.7 (including python 3+)


Client Features

Server Features

Use Cases

Although most system administrators will find little need for a Modbus server on any modern hardware, they may find the need to query devices on their network for status (PDU, PDR, UPS, etc). Since the library is written in python, it allows for easy scripting and/or integration into their existing solutions.

Continuing, most monitoring software needs to be stress tested against hundreds or even thousands of devices (why this was originally written), but getting access to that many is unwieldy at best. The pymodbus server will allow a user to test as many devices as their base operating system will allow (allow in this case means how many Virtual IP addresses are allowed).

For more information please browse the project documentation

Example Code

For those of you that just want to get started fast, here you go:

from pymodbus.client.sync import ModbusTcpClient

client = ModbusTcpClient('')
client.write_coil(1, True)
result = client.read_coils(1,1)

For more advanced examples, check out the examples included in the respository. If you have created any utilities that meet a specific need, feel free to submit them so others can benefit.

For questions visit pymodbus-google-group or gitter

Pymodbus REPL (Read Evaluate Procee Loop)

Starting with Pymodbus 2.x, pymodbus library comes with handy Pymodbus REPL to quickly run the modbus clients in tcp/rtu modes.

Pymodbus REPL comes with many handy features such as payload decoder to directly retrieve the values in desired format and supports all the diagnostic function codes directly .

For more info on REPL refer Pymodbus REPL



You can install using pip or easy install by issuing the following commands in a terminal window (make sure you have correct permissions or a virtualenv currently running):

easy_install -U pymodbus
pip install  -U pymodbus

To Install pymodbus with twisted support run:

pip install -U pymodbus[twisted]

To Install pymodbus with tornado support run:

pip install -U pymodbus[tornado]

To Install pymodbus REPL:

pip install -U pymodbus[repl]

Otherwise you can pull the trunk source and install from there:

git clone git://
cd pymodbus
python install

Either method will install all the required dependencies (at their appropriate versions) for your current python distribution.

If you would like to install pymodbus without the twisted dependency, simply edit the file before running easy_install and comment out all mentions of twisted. It should be noted that without twisted, one will only be able to run the synchronized version as the asynchronous versions uses twisted for its event loop.

Current Work In Progress

Since I don’t have access to any live modbus devices anymore it is a bit hard to test on live hardware. However, if you would like your device tested, I accept devices via mail or by IP address.

That said, the current work mainly involves polishing the library as I get time doing such tasks as:

Development Instructions

The current code base is compatible with both py2 and py3. Use make to perform a range of activities

$ make
   Makefile for pymodbus


 make install    install the package in a virtual environment
 make reset      recreate the virtual environment
 make check      check coding style (PEP-8, PEP-257)
 make test       run the test suite, report coverage
 make tox        run the tests on all Python versions
 make clean      cleanup all temporary files 


Just fork the repo and raise your PR against dev branch.

License Information

Pymodbus is built on top of code developed from/by:
  • Copyright (c) 2001-2005 S.W.A.C. GmbH, Germany.
  • Copyright (c) 2001-2005 S.W.A.C. Bohemia s.r.o., Czech Republic.
  • Hynek Petrak,
  • Twisted Matrix

Released under the BSD License