Write desktop and web apps in pure Python
Python JavaScript
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* force new enough pscript, and update pypy ci

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Latest commit 356af9d Aug 3, 2018



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Notice: Flexx has recently been refactored, improving Flexx on many fronts (e.g. make it scale better). Note that the API has changed in several ways though! We're now moving towards a release that brings us to beta status.

Want to stay up-to-date about Flexx? Subscribe to the NEWS issue.


Flexx is a pure Python toolkit for creating graphical user interfaces (GUI's), that uses web technology for its rendering. Apps are written purely in Python; Flexx' transpiler generates the necessary JavaScript on the fly.

You can use Flexx to create (cross platform) desktop applications, web applications, and (if designed well) export an app to a standalone HTML document. It also works in the Jupyter notebook.

The docs are on Readthedocs. the code is on Github. Flexx is currently in alpha status; any part of the public API may change without notice. Feedback is welcome.


Click the image below for an interactive example:


There is a demo server at http://demo.flexx.app .


The primary motivation for Flexx is the undeniable fact that the web (i.e. browser technology) has become an increasingly popular method for delivering applications to users, also for (interactive) scientific content.

The purpose of Flexx is to provide a single application framework to create desktop applications, web apps, and (hopefully soon) mobile apps. By making use of browser technology, the library itself can be relatively small and pure Python, making it widely available and easy to use.


Flexx requires Python 3.5+ and also works on pypy. Further, it depends on:

  • the tornado library (pure Python).
  • the PScript library (a flexxui project).
  • the webruntime library (a flexxui project).
  • the dialite library (a flexxui project).

For running desktop apps, it is recommended to have Firefox installed.

The current release is really old, please use the latest master if you want to try it:

  • pip install https://github.com/flexxui/flexx/archive/master.zip, or
  • Clone the repo and add it to your PYTHONPATH.

When version 0.5 is released:

  • conda install flexx -c conda-forge, or
  • pip install flexx


Flexx makes use of the liberal 2-clause BSD license. See LICENSE for details.