[Contributing] Mentions string.format, are f-strings allowed?

[eddiebergman]

Hiyo,

Just reading the contributing guide and in the sections it mentions about the pep8 guidelines, it doesn't mention f-strings. I would imagine these are allowed and we should add a section to CONTRIBUTING.md?

[PGijsbers]

F-strings are the preferred way to format strings since a few years, but we didn't go an change old-style formatting unless a PR affected them. Might be useful to just run something like flynt (no experience using it) to convert all strings.