Fix flake8 errors on Python 3.x

9 jobs for master in 10 minutes and 19 seconds (queued for 1 second)
Status Job ID Name Coverage
  Prepare
passed #19944
docker-host
build build-env image

00:00:02

passed #19946
docker-host
build phoenix 4.10 image

00:00:02

passed #19945
docker-host
build phoenix 4.11 image

00:00:02

passed #19948
docker-host
build phoenix 4.8 image

00:00:01

passed #19947
docker-host
build phoenix 4.9 image

00:00:02

 
  Test
passed #19950
docker
test phoenix 4.10

00:10:11

passed #19949
docker
test phoenix 4.11

00:10:14

passed #19952
docker
test phoenix 4.8

00:10:05

passed #19951
docker
test phoenix 4.9

00:10:10