We exclude some PEP8 checks so that they do not emit warnings/errors, see setup.cfg.
The recommended procedure to improve this is to:
wait for a time with little parallel development activity (avoid causing merge conflicts just because of fixing pep8 stuff)
remove one item from pep8ignore list
fix all places where it occurs, commit.
E501 is currently disabled as the pytest-pep8 we have to use does not support setting pep8maxlinelength in setup.cfg. As soon as it does, we can set 120 and enable it for most source files.