legacy: rename lookup_errors to not be in all caps (flake8 warning) flake8 has a plugin, pep8-naming, which is not installed by default, but is used if available, no extra config required. This plugin checks names of variables, classes, functions and so on against PEP-8, and it complained about this variable: N806 variable in function should be lowercase Since this isn't a module-level constant, but just a helper variable used only in one function, it's fine to just rename it. With this error gone, flake8 output (used plugins: mccabe, naming, pycodestyle, pyflakes) is totally clean.