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Dropping Python 2 Support #62

Closed gsnedders closed 3 years ago

gsnedders commented 3 years ago

Mostly filing an issue here to at least have somewhere to write down the current Python 3 plan.

The status quo is most of our infrastructure now works on Python 3, and work is ongoing to fix the rest.

Most of us working on the infrastructure would like to minimise the amount of time we're supporting both Python 2 and Python 3, and we should probably have a discussion about both timeline for dropping Python 2 and what the minimum version of Python 3 we want to support is.

My suggestion (made privately earlier this week) was that we target 1 Jan 2021 for Python 3 only. In the immediate short term, we expect to keep the codebase in a state where Python 2 support could be trivially reintroduced, likely by simply making Python 2 supported on a "PRs welcome" basis but with no ongoing testing. In the relatively near future, maybe as soon as a month later (i.e., 1 Feb 2021), we will then start accepting PRs that will break Python 2 support significantly (e.g. replacing the comment based type annotation syntax with the Python 3 annotation syntax).

As for minimum version of Python 3, I have been assuming that we will be wanting to support Python 3.6 (as this is packaged in Ubuntu 18.04 LTS) but not Python 3.5 (note that this is dropping Debian Stretch—currently oldstable—released in 2017 and with LTS till 2022). Python 3.6 was a relatively significant release, with f-strings, stabilization of asyncio, variable annotations and more.

stephenmcgruer commented 3 years ago

Thanks for filing this Sam. My intention was that @ziransun and I will work on filing an RFC in the next few weeks for this, as we are close to having every (known) Py3 problem either fixed or at least explained.

As for minimum version of Python 3, I have been assuming that we will be wanting to support Python 3.6 ...

Agreed; I have always thought of our initial support as being 3.6 and 3.8+. We would likely continue to run unittests/etc on both versions for the foreseeable future, but the WPT test suite itself would run on 3.8 in WPT CI.

Re the timeline; switching to Py3-first (i.e. switch the WPT test suite runs over to Py3) in Q4 and then Py3-only in Q1 has been my hope. I didn't expect to get Py3-only as soon as Jan 1st, but I'd be happy to see it happen :).

jgraham commented 3 years ago

I would say that we should aim to have our CI and major vendor CI running in Py3 by 2021-01-01 but should continue to support Py2 in our CI for some time after that in case we find a reason to roll back. At a minimum I'd say a 2021-02-01 to actually drop Py2 support and start to accept Py3-only patches.

jgraham commented 3 years ago

Alternatively if people are comfortable with the more aggressive timeline, we could aim for out CI and vendor CI to switch before 2020-12-1. But I still have concerns that there's a lot of code not on the critical path to running tests (e.g. metadata update code) that is untested in Py 3.

Hexcles commented 3 years ago

To consolidate everyone's suggestions so far, what about the following concrete timeline:

I also agree we should only support Python 3.6+.

gsnedders commented 3 years ago

What's the current status of this?

jgraham commented 3 years ago

Just landed a PR that starts removing some Py 2 support. I understood that we had agreed the 3.6+ starting 2021-02-01 timetable. I'm going to close this issue but feel free to reopen.

gsnedders commented 3 years ago

Just landed a PR that starts removing some Py 2 support. I understood that we had agreed the 3.6+ starting 2021-02-01 timetable. I'm going to close this issue but feel free to reopen.

I couldn't find any citation that: a) we did ultimately agree that; b) that we actually were holding ourselves to that (given some of the earlier delays).

stephenmcgruer commented 3 years ago

I couldn't find any citation that: a) we did ultimately agree that; b) that we actually were holding ourselves to that (given some of the earlier delays).

I have been going based on https://github.com/web-platform-tests/rfcs/blob/master/rfcs/py_3.md (associated PR https://github.com/web-platform-tests/rfcs/pull/69), combined with the fact that no vendor had asked for an extension. (Including Chromium, despite the fact that I have had to solve 2-3 medium level fires over the last two months when trying to upgrade).

EDIT: Unless you mean the 'minimum level 3.6' part, in which case fair point that (outside of the lack of disagreement above) I don't think we actually officially stated that. I would be happy to LGTM an edit to the py_3.md RFC to do so, myself.

jgraham commented 3 years ago

Yeah I was also assuming that the merged RFC held (despite also having to fix some problems with gecko to make the timetable work).

gsnedders commented 3 years ago

Ergh, I missed it while scrolling through the list of RFCs!