After having taken a stab at fixing a couple of issues within the main CPython implementation of Python, I decided whilst waiting for some of those pull requests to be merged I might try to contribute to some other open source projects in the Python ecosystem that are endorsed by the PSF.

Lewis suggested taking a look at Beeware, which recently received a grant from the PSF Education group to improve support for Python on Android, as part of their mission to enable cross-platform Python-based native apps.

Getting Started

There’s a lot of pieces to Beeware that are in early stages of development and support, and should be ripe for further contribution. However, the first stages revolved primarily around familiarising myself with the ecosystem to understand which pieces would be most suitable.

Beeware has several constituent projects, some of the relevant ones are:

  • toga: a cross-platform native widget toolkit, that provides a high-level API wrapping the concept of an App, allowing users to build GUI applications which resolve to using native widgets on the target platform

  • colosseum: an implementation of the CSS specification for resolving positions and locations of elements on a canvas, used by toga for styling applications

  • voc: a transpiler which converts Python bytecode allowing Python to be compiled into Java bytecode and run on the JVM, enabling Android native apps

  • batavia: an implementation of the Python virtual machine in Javascript, enabling Python bytecode to run on the browser or over node.js

The one which is most obviously approachable starting from a background of just Python (as opposed to native widget libraries like Cocoa, GTK+, or Java and Javascript) is colosseum, which is a complex problem but well-defined, and comes with a suite of (currently failing) tests which verify it meets the CSS specification.

Attempting to Contribute

As suggested on the colosseum contributing guide, I selected a test (at random) from the list of “known failures” and removed it. Re-running the tests, I took a look at what exactly fails as part of the test.

What I found was not particularly amenable to a contribution: it appears that an implementation of an object expects a certain class which depending on the type of the object would contain a certain field. But for the main layout API, this object was always being passed in as None, seemingly because that whole class of objects hadn’t been implemented:

def layout(display, node, standard=HTML5):
    containing_block = Viewport(display, node)
    font = None  # FIXME - default font


    # 10.1 1
    layout_box(display, node, containing_block, containing_block, font)

Note the FIXME. It appears that a lot of the current issue with colosseum is simply missing functionality: code which has been written in a certain way (knowing it will be needed to meet the CSS spec) but is being fed by defaults and stubs.

This represents both a difficulty and an opportunity: once the requirements are understood, and the problem fleshed out (probably via interacting with the core devs) there is certainly clear work to be done which just requires skills already available to our team, designing and coding Python.

After talking to some of the core devs on the gitter, I’m somewhat hopeful that they’ll be able to direct us at some work to be done, which might represent good group projects for further contribution in the New Year.