* #3847 fix handling of non-ASCII characters in swap_case

* #3847 remove unused regex

* Fix formatting (with black) Fixes: #3847

* Add type hints for `swap_case` function
Co-authored-by: NFrank Schmitt <frankschmitt@gmx.de>
Co-authored-by: NDhruv Manilawala <dhruvmanila@gmail.com>