support for python 3.10

[richvdh]

Python 3.10.0 final was released 3 months ago, on 2021-10-04. We should add support for it.

[richvdh]

I think this involves:

• adding 3.10 to the list of default environments in tox.ini (already done in Drop EOL python 3.6 from CI #11595)
• adding 3.10 to the list of distributions we run trial tests on (already done in Run CI with Python 3.10 and Postgres 14 #10992)
• building new sytest docker images which include python 3.10 (I think we could use Debian 'bookworm' as a basis for this) and adding it to the list for CI (Add support for testing on Python 3.10 sytest#1184)
• updating https://matrix-org.github.io/synapse/develop/setup/installation.html#installing-as-a-python-module-from-pypi to note 3.10 is now supported.
• adding 3.10 to the list of classifiers in setup.py (Advertise Python 3.10 support in setup.py #12111)
• following the y-1 rule suggested at Decision Needed: Default to a newer Python in our Dockerfile? #8674 (comment), it's time to update the docker images to python 3.9. (Use Python 3.9 in Synapse dockerfiles by default #12112)

[DMRobertson]

• adding 3.10 to the list of distributions we run trial tests on (already done in

See also #10992

[anoadragon453]

building new sytest docker images which include python 3.10 (I think we could use Debian 'bookworm' as a basis for this) and adding it to the list for CI

It looks like this last remaining item was done in matrix-org/sytest#1184, and indeed we now have bookworm images on DockerHub.

With that final box ticked, can this issue be closed?

[richvdh]

yes, if you open a new one to track:

Relatedly, following the y-1 rule suggested at #8674 (comment), it's time to update the docker images to python 3.9.

:)