What should I do if I want to make a library Brython-compatible?

This is a subset of #491 that is focused specifically on libraries that might want to run on both Brython and CPython without much difference in functionality; things for implementing data structures, file formats, etc.

Writing Python code in the manner that I am accustomed to—particularly to take advantage of the “same language as the backend” feature that Brython offers—would require using tons of libraries that are currently broken on Brython. To get those fixed we’ll need to add continuous integration to tons of projects.

As an open-source library author, if I want to support a different runtime such as PyPy, I usually just drop a new environment into my tox.ini, then run my tests as I did previously, with the same runner.

However, the best practice for doing this on Brython is somewhat unclear - there have been a few interesting blog posts about testing an application using Selenium or whatever, but for libraries like automat https://github.com/glyph/automat/issues/124 that don’t have any UI features but might just be useful utilities within the browser… what’s the first step?

I tried to proof-of-concept this with a custom unittest runner via https://github.com/glyph/brytly/blob/0d7c313830e3fc1ddf71986dec1473df048b6ae4/brytly/phantestic.py / https://github.com/glyph/brytly/blob/0d7c313830e3fc1ddf71986dec1473df048b6ae4/brytly/phantestic.js but this was always a pretty brittle hack and was pretty invasive - it required using this specific test fixture class.

Getting something like pytest to work within brython I would imagine would be a major challenge in its own right, but even if we’re going to stick just to stdlib unittest for the sake of compatibility it seems like forcing users to use an incomplete reimplementation for their base class is going to be a non-starter for most projects.

[PierreQuentel]

@glyph I’m not sure to understand; unittest is actually supported by Brython. I have developed an interface to run some of the tests in the CPython test suite (at /tests/unittests/index.html), with an adapted version of HTMLTestRunner. It’s not super fast, but shows that a unittest-based test suite developed for a CPython application can be used unmodified in Brython.

[Frick-David]

+1 on question. Hoping to get brython working with plotly.js