[Python-Dev] Re: PEP 654 -- Exception Groups and except* : request for feedback for SC submission

The "no subclasses" seems pretty severe, particularly if you can't even use marker attributes because it isn't clear when a different instance of container ExceptionGroup will be substituted. The justification for this restriction was that .split() had to be be able to instantiate ... wouldn't it be enough to just say that subclasses need a compatible __init__ and __new__ for that reason, and then leave it to consenting adults? -jJ