Integrating new code quality tools into existing legacy is always hard.

Here's a good article about integrating RuboCop into existing #ruby code.

We are also working on adding a single command integration of wemake-python-styleguide into an existing #python legacy. Currently it is a WIP, but you can already read about it here: https://github.com/wemake-services/wemake-python-styleguide/pull/1276/files#diff-a767531552fe775f5be950388425b154R28

More tools and articles about this to come!