Thank you Sergev Finer for finishing the implementation of my PEP 446. Supporting to only inherit a set of Windows handles was a "small note" my PEP 446, mostly because I didn't feel able to implement the feature, but also because we still supported Windows versions which didn't implement this feature (PROC_THREAD_ATTRIBUTE_HANDLE_LIST) if I recall correctly.

Thanks Eryk Sun, Gregory P. Smith and Steve Dower for the reviews and help on getting this nice feature into Python 3.7!