Commons Mass Description contains some lint errors catched by flake8 (the list is on the bottom of the task) that are currently ignored, see https://github.com/wikimedia/labs-tools-commons-mass-description/blob/master/tox.ini.
# How to fix an error
(all paths here are from the root of the repository)
# Choose an error from the list below
# Delete the error and its comment from /tox.ini
# Run tox -e lint to run only lint and see where the error is
# Fix the error reported by the command until the command from step 3 reports no errors.
$ tox -e lint | grep '^\.' | sed 's/: /@/g' | cut -d @ -f 2 | sed 's/^ //g' | sort | uniq -c | sort -k1,1nr -k2
21 E302 expected 2 blank lines, found 1
6 E122 continuation line missing indentation or outdented
3 E101 indentation contains mixed spaces and tabs
1 E721 do not compare types, use 'isinstance()'