Thank you for taking time to contribute to OpenWPM!
Some development pointers
See https://github.com/mozilla/OpenWPM#development-pointers.
Avoid failing tests for PRs caused by formatting/linting issues
This shows up in Travis as The command "flake8" failed and exited with 1 during . and is preceded by the various formatting/linting issues that flake has detected.
You can use a combination of isort and autopep8 to fix errors automatically in-place before you submit your PR:
python -m isort -rc --skip venv .python -m autopep8 -r --in-place --exclude venv .
(The latter requires that the development dependencies are installed.)
Not all errors will be fixed automatically, and sometimes the above commands will change files that are not relevant to your PR. Revert those changes and only include (automatic and manual) changes that are related to the code you are modifying by your PR.