python 2 end of life coordination

Python 2.7.18 has just been released. It is the last Python 2 release that will ever happen, and Python 2 is now unsupported, end of life, dead.

It is likely that the next Debian release (bullseye) will not support Python 2 at all. It's also possible the current release (buster) does not support Python 2 for security issues forever. So we have some time, in practice, to handle this problem. But we definitely will need to finish this migration before some time around 2022, and the sooner the better.

Until then, we need to figure out a strategy on how to handle that transition. Some of our code has been written for Python 3, but we have a large amount of Python-2-only code that is running, in multiple places. Some of it is TPA's responsibility, but other code is ran by teams or service admins.

Since we run stretch or buster everywhere, we're in a good position to not have to support both Python 2 and Python 3 at once: we can just migrate to python 3. Stretch has Python 3.5 so we could target that as a minimum version. But we could also assume we will have completed the Buster upgrade by then and just target the more featureful Python 3.7.

In any case, we need a plan for this and it would be wise to do it before we're backed into a corner.

Some resources:

• http://python3porting.com/ - python 3 porting book, freely available
• https://python3statement.org/practicalities/ - some more advice on porting
• https://docs.python.org/3/howto/pyporting.html - upstream guide, which still recommends supporting python 2.7