(Put an X inside the [ ] to denote check mark [X].)

• If creating a new file :

  • added links to it in the README files ?
  • included tests with it ?
  • added description (overview of algorithm, time and space complexity, and possible edge case) in docstrings ?

• if done some changes :

  • wrote short description in the PR explaining what the changes do ?
  • Fixes #479 if related to any issue

• other

This fixes issue #479 if you would like to add black in the CI.

It will not make every build (from this PR) fail in the CI but log all files that would be reformatted. In order to install black during CI, it was necessary to drop python 3.5 as black needs python 3.6.0+