Since we drop Python 3.5 support (#240), we can use the `f-string` format everywhere. #### What is f-string - https://www.blog.pythonlibrary.org/2018/03/13/python-3-an-intro-to-f-strings/ - https://cito.github.io/blog/f-strings/ #### Todo - [x] #403: A part has been done by `pyupgrade`. - [x] Convert manually `.format()`, `%`, and `str + str` formats to `f-string` format. Try to keep the f-string readable by not putting a too big operation in the f-string. For logging, keep `%` format for now, since it causes issues with Pylint and mypy.