Open Stack

We've talked a bit about migrating to Python 3, but (unless I missed it) 
not a lot about which version of Python 3. Currently all projects that 
support Python 3 are gating against 3.5. However, Ubuntu Artful and 
Fedora 26 already ship Python 3.6 by default. (And Bionic and F28 have 
been released since then.) The one time it did come up in a thread, we 
decided it was blocked on the availability of 3.6 in Ubuntu to run on 
the test nodes, so it's time to discuss it again.

AIUI we're planning to switch the test nodes to Bionic, since it's the 
latest LTS release, so I'd assume that means that when we talk about 
running docs jobs, pep8 &c. with Python3 (under the python3-first 
project-wide goal) that means 3.6. And while 3.5 jobs should continue to 
work, it seems like we ought to start testing ASAP with the version that 
users are going to get by default if they choose to use our Python3 
packages.

The list of breaking changes in 3.6 is quite short (although not zero), 
so I wouldn't expect too many roadblocks:
https://docs.python.org/3/whatsnew/3.6.html#porting-to-python-3-6

I think we can split the problem into two parts:

* How can we detect any issues ASAP.

Would it be sane to give all projects with a py35 unit tests job a 
non-voting py36 job so that they can start fixing any issues right away? 
Like this: https://review.openstack.org/572535

* How can we ensure every project fixes any issues and migrates to 
voting gates, including for functional test jobs?

Would it make sense to make this part of the 'python3-first' 
project-wide goal?

cheers,
Zane.


(Disclaimer for the conspiracy-minded: you might assume that I'm 
cleverly concealing inside knowledge of which version of Python 3 will 
replace Python 2 in the next major release of RHEL/CentOS, but in fact 
you would be mistaken. The truth is I've been too lazy to find out, so 
I'm as much in the dark as anybody. Really. Anyway, this isn't about 
that, it's about testing within upstream OpenStack.)