Being pure Python and cross platform, it should work (almost) anywhere where there’s Python and a browser. Flexx is written for Python 3, but can also be installed on legacy Python (Python 2.7). It also works on Pypy. Flexx actively supports Firefox, Chrome and (with minor limitations) IE/Edge.
pyscrip subpackages require no
ui subpackages require Tornado (a
pure Python package) and a browser. To run apps that look like desktop
apps, we recommend having Firefox installed.
Developers that want to run the tests need:
- pytest and pytest-cov (get them via conda or pip)
- flake8 (get it via conda or pip)
Flexx is in development and is in alpha status. Any part of the public API may change without notice. Status of subpackages:
flexx.pyscriptmodule is in a good state and has ~ 100% test coverage.
flexx.eventmodule recently received an overhaul. Minor tweaks can be expected.
flexx.webruntimemodule works well, but needs tests and should support more runtimes.
flexx.appmodule is increasingly stable.
flexx.uimodule is stabalizing and most changes will be related to the addition of new widgets.
conda install flexx -c conda-forge
pip install flexx
- Old school:
python setup.py install
- Clone the repo and add the root dir to your PYTHONPATH (developer mode, not possible for Python 2.7)
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 and web apps. By making use of browser technology, the library itself can be relatively small and pure Python, making it widely and easily available.
Libraries written for Python, but not in Python have a much harder time to survive, because users don’t easily become contributors. This is one of the reasons of the success of e.g. scikit-image, and the demise of e.g. Mayavi. Since Flexx is written in a combination of Python and PyScript, its user community is more likely to take an active role in its development.
Flexx is designed to be modular, and this is reflected in the package
layout. The most commonly used subpackage is
flexx.ui. However, the
technologies on which it relies are defined in separate subpackages,
which are independent from each-other, and can be used by themselves.
import flexx.webruntime only imports that subpackage, and not
the whole ui toolkit and app framework (nor Tornado).
The image above outlines the structure of Flexx. The sole purpose of
the webruntime module is to launch a runtime to execute the app in.
This can be a browser, or a XUL application that looks like a desktop
The event module provides a powerful property and event system that
makes it easy to connect different parts of your application.
The pyscript module provides a system for translating Python code to
In the app module the app mainloop is defined, running the server to
which the web runtime connects (via a websocket). Further, it combines
the event and pyscript functionalities into the
a class for which its instances have a corresponding representation in
to define methods for the JS version of the object in Python code (or
PyScript, to be precise). This is the base class for all widgets, but
could in principle also be useful in other situations where a tight
connection between Python and JS is required.
In the ui module all widgets are implemented.
In this documentation, we include a separate reference for each subpackage. We recommend starting with the ui module, and not to worry about the other modules until they’re needed.