Is there any reason that this change should be affecting what tests we're running? Codecov.io is showing a lot of changes, and it doesn't look spurious.

It looks like appveyor did not fire, maybe this is the coverage we get only from appveyor?

Might be that we need to take care of flake8 also in the other branches (e.g. it's failing in this backport #13340).

@meeseeksbot backport to v3.0.x

@meeseeksdev backport to v3.0.x

Owee, I'm MrMeeseeks, Look at me.

There seem to be a conflict, please backport manually. Here are approximate instructions:

1. Checkout backport branch and update it.

$ git checkout v3.0.x
$ git pull

1. Cherry pick the first parent branch of the this PR on top of the older branch:

$ git cherry-pick -m1 68e8d9543abce31da04a79970fdfb5dea914a540

1. You will likely have some merge/cherry-pick conflict here, fix them and commit:

$ git commit -am 'Backport PR #13337: Bump to flake8 3.7.'

1. Push to a named branch :

git push YOURFORK v3.0.x:auto-backport-of-pr-13337-on-v3.0.x

1. Create a PR against branch v3.0.x, I would have named this PR:

"Backport PR #13337 on branch v3.0.x"

And apply the correct labels and milestones.

Congratulation you did some good work ! Hopefully your backport PR will be tested by the continuous integration and merged soon!

If these instruction are inaccurate, feel free to suggest an improvement.

OK, I'll put it in #13418.

Thanks @QuLogic !