Those of you who work on a fairly large project will have noticed that running flake8 over all of it takes some time, and that this slows down development. Nova (at least) has a solution to this, in the form of a "fast8" tox environment that runs flake8 only against the files that have changed in the latest patch + the working directory. This is *much* faster, but that approach has some limitations: the script is buggy, it only tests the top-most patch, it creates a second tox environment (which is slow) that can then get out of sync with your regular pep8 environment, and of course it requires the project to add it explicitly. If you're interested in a solution with none of those limitations, here is a script that I've been using: https://gist.github.com/zaneb/7a8c752bfd97dd8972756d296fc5e41f It tests all changes on the branch, using your existing pep8 tox environment, handles deleted files and changes to non-python files correctly, and should be usable for every OpenStack project. I hope this is helpful to someone. (Note that the pep8 environment on many projects includes other test commands in addition to flake8 - such as bandit - so you should still run the pep8 tox tests once before submitting a patch.) cheers, Zane.