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Re: Removing Python 2 support in OpenStack [was: Please do not drop Python 2 modules]

On 04/25/2018 09:39 AM, Ondrej Novy wrote:
> Hi,
> 2018-04-25 9:06 GMT+02:00 Thomas Goirand <zigo@xxxxxxxxxx
> <mailto:zigo@xxxxxxxxxx>>:
>     I would like to start dropping Python 2 as early as possible though. The
>     only question that remains is: how many people still have Python 2 only
>     code using clients.
> /me
> And because:
>  1. OS clients are already packaged for Py2 now
>  2. upstreams official supports Py2 now (and probably will support in OS
>     release targeted for Buster)
>  3. Python 2 will be in Buster
> I didn't see any real benefits dropping them before Buster release.
> Let's drop them just after Buster release.

I would have preferred if we had this discussion in our own list,
however since you've started it here, let's do it. I'm adding the
OpenStack list just for the archive.

I'd love to get the removal of Python 2 prepared for the next OpenStack
release, Rocky, due for next August, and which will be the OpenStack
release for Buster. I see a lot of real benefits. Here's a few of them
which are popping now, but I don't think it's exhaustive:

- faster build time (no need to test with Python 2, so less chances of
build failure).

- no chance to have any Python 2 packages installed, so we're sure we're
on a full Python 3 stack (in my current setup, unfortunately some Python
2 packages are still pulled). This may go on for another 3 years if we
don't remove Python 2 now, with the added issue that it will pull
*older* version of clients if selecting Python 2 and if we still have
them in Buster (ie: case of OpenStack backports on top of Stable).

- packaging and decrufting will take a long time, so we'd better start
early. Especially if we want to do it the proper way, without breaking
any reverse (build-)dependency that are outside of OpenStack.

- at some point, even upstream will move to Python 3, and Python 2 will
be the legacy old thing. Do we really want to be the only distribution
that will hit these Python 2 bugs? In such case, we'll be alone writing
these Python 2 bugfix patches. :/

- Other distros (RHEL and Ubuntu) will move to Python 3 only in the next
OpenStack development cycle, meaning we'll be alone with Python 2
support at some point.

The other thing is, it's ready! I was able to do functional testing on
top of the Python 3 release of OpenStack Debian packages. So why should
we hold any longer?

The only benefit we get with keeping Python 2 support is for thirdparty
software that is still using Python 2. We don't have this in Debian at
the moment. What's the status in your company? Do you still need Python
2 for your internal use? What's the ETA for switching to Python 3?


Thomas Goirand (zigo)