Drop Python 2 support

[foolip]

pywebsocket3 depends on six, and while it's very unlikely to be the last indirect six dependency in web-platform-tests/wpt#28776, perhaps can be dropped?

Is pywebsocket3 used outside of WPT, or can it just go with Python 3.6+ like WPT?

[ricea]

It's still used in at least Chrome's web_tests and WebKit's layout tests. I don't think we can drop Python 2 support just yet, but we might be close.

An option might be to pin Python 2 support at a particular version, and remove it from later versions, but I'd prefer not to do that as it could backfire badly.

I'm going to keep this open as a task to do when the known downstreams are ready.

[foolip]

Are we still using Python 2 in Chromium CI? For WebKit, @gsnedders was OK with dropping py2 support for WPT itself on Feb 1 this year, which happened, but maybe pywebsocket3 is also used in contexts outside of WPT in Chromium/WebKit CI?

@jgraham do you know if this is used in Gecko outside of WPT?

[ricea]

Yes, pywebsocket3 is still run under Python 2 for the tests located in https://source.chromium.org/chromium/chromium/src/+/main:third_party/blink/web_tests/http/tests/websocket/. From my skimming of the code, it looks like all of run_web_tests.py apart from wptserve run under Python 2 still. I think it should be possible to switch only pywebsocket3 over using a similar technique, however the last time I tried this I was not successful.

[foolip]

I see, so this isn't a quick fix then. But now there's an issue that can grow old before finally being resolved :)

[jgraham]

We seem to have another vendored copy for mochitests, which are apparently still running under Py2 in CI. But that is supposed to change soon and we could upgrade that copy seperately from the copy in wpt which we're using with Py3 exclusively.

[Anutrix]

Any updates on this? I still see that six is used and this seems to be blocker in a project that's trying to get rid of six.
Also, is this project maintained?

Will it be reviewed if I make a PR to remove six and/or update code to Python 3?

[ricea]

No progress to report, sorry. The blockers in Chromium to dropping Python 2 support are gone. I don't know about other projects, but I assume that active projects have had to move away from Python 2 as CI infrastructure stops supporting it.

pywebsocket3 is maintained and in active use, but the project owners don't have a lot of time to devote to it.

If you can make a PR that would be a big help and I will certainly review it. If possible I would like "necessary changes to stop using six" and "cleanups unlocked by not supporting Python 2" to be split into separate PRs so I can prioritise reviewing the essential stuff first.

I want to bump the major version number to reflect that it's a breaking change.