Flexx is a pure Python toolkit for creating graphical user interfaces (GUI's), that uses web technology for its rendering. You can use Flexx to create desktop applications, web applications, and (if designed well) export an app to a standalone HTML document. It also works in the Jupyter notebook.

Being pure Python and cross platform, it should work anywhere where there's Python and a browser. To run apps in desktop-mode, we recommend having Firefox installed.

Flexx has a modular design, consisting of a few subpackages, which can also be used by themselves:

• ui - the widgets
• app - the event loop and server
• react - reactive programming (how information flows through your program)
• pyscript - Python to JavaScript transpiler
• webruntime - to launch a runtime

Working code example::

from flexx import app, ui, react
    
class Example(ui.Widget):
    
    def init(self):
        self.count = 0
        with ui.HBox():
            self.button = ui.Button(text='Click me', flex=0)
            self.label = ui.Label(flex=1)
    
    @react.connect('button.mouse_down')
    def _handle_click(self, down):
        if down:
            self.count += 1
            self.label.text('clicked %i times' % self.count)

main = app.launch(Example)
app.run()

Flexx is still very much a work in progress. Please don't go use it just yet for anything serious. The public API can change without notice. However, we're interested in feedback, so we invite you to play with it!

• Clone the repo and add it to your PYTHONPATH, or python setup.py install, or pip install flexx.
• Run the examples.
• Read the docs.

There is an Amazon instance running some demos on http://52.21.93.28:8000/ (unless I turned it off for testing, etc.).