Generated by `pyupgrade --py3-plus --keep-percent-format` on all our
Python code except `zthumbor` and `zulip-ec2-configure-interfaces`,
followed by manual indentation fixes.
Signed-off-by: Anders Kaseorg <anders@zulipchat.com>
This requires part 1 (which can take hours to run but generally
doesn't require downtime) to be completed first.
This portion of the migration will require the server to be completely
down for a brief period; for chat.zulip.org with 250M UserMessage
rows, it took about 60s to run; that time will vary depending on
hardware details like whether the server has an SSD, but fundamentally
shouldn't be long.
Our upgrade-zulip and upgrade-zulip-from-git tools can apply this
migration correctly; nothing special needs to be done.
Fixes#13040.
Anders Kaseorg
Mateusz Mandera