Code review comment for ~jslarraz/review-tools:add-pre-commit-hook

@emitorino running checks only on changed files is mainly done for efficiency as you can only introduce format issues on files you are effectively modifying (hopefully). If by "older issues" you mean the code that didn't follow the black convention, it was reformatted on https://code.launchpad.net/~jslarraz/review-tools/+git/review-tools/+merge/465415, if it is anything else, please let me know to take a look :)