widgets

Example jupyter kernel with ipywidgets

This example implements the ipywidgets widget protocol version 2, as well as a few of its widgets. It also comes with a little toy language to try out the widgets. It serves as an example how to setup the widgets and communicate to the frontend.

What is in the example

Models

Almost all the models defined in ipywidgets. These models define the messages sent between frontend and backend.

Widgets

Currently only the following widgets are supported:

• FloatSliderModel
• IntSliderModel
• ButtonModel
• CheckboxModel

You can easily extend the set by registering them in the WidgetFactory defined in the app.d

Repl

This example also contains a small repl to construct the widgets, and comes with autocomplete support. See the Example.ipynb for more information.

Limitations

• Changes to a widgets state must be synchronized manually by calling onRequestState() on the widget.

• The toy language only supports int, doubles and strings.

• The example has not implemented support for binary data.

How it works

You can read up on the version 2 of the ipywidgets widget messaging protocol here.

Briefly, it works as follows:

• upon creation of a Widget in the backend, it sends a commOpenMessage (for each model), with a comm_id referencing this widget
• to send updates to the frontend, it sends the commMessage with the modified state
• to display the widget, it send the displayDataMessage
• the frontend in turn sends commMessage's for each change

Using it in your own backend

Most likely you will have your own interpreter in your backend, but you can reuse much of the following code:

• models.d is a freestanding file and defines most of the ipywidgets models.
• widgets.d depends on models.d and implements the state synchronisation with the frontend.
• app.d contains the commOpen/commClose/commMessage functions that you will need to implement as well.

Connecting to other widgets

There are plenty of open source widgets available such as bqplot, pythreejs and ipyleaflet

If you already have the ipywidgets in your backend, then you will only need to implement the models that correspond with the models of those widgets.

Write the complete Widget in D

With D's support for WebAssembly it is possible to write a custom widget completely in D. See the skoppe/spasm-jupyter-widget-example for an example.

Run it yourself

To install locally, copy kernel.json from this directory to ~/.local/share/jupyter/kernels/<name>/kernel.json (linux) or ~/Library/Jupyter/kernels/<name>/kernel.json (mac). The directory name can be anything. The widgets_example_kernel executable build by dub will have to be in the PATH, otherwise edit kernel.json to point to the path where it is located.

To install globally, use /usr/share/jupyter/kernels (linux and mac) instead of ~/.local/share/jupyter/kernels.

And that's it. When you run jupyter notebook you'll see jupyter-wire-widgets-example as one of the available kernels. The example here contains a toy programming language with widgets.

See the Example.ipynb notebook.

Make sure to install ipywidgets 7.0 first.