[Python-ideas] Use `isinstance` check during exception handling

[Emanuel Barry]

I think the main concern here is not "Would that benefit the corner cases?" - it surely would. What we should be worrying is, "Will this impede the common cases?". I think that it should be possible, for all the (very) common cases, to use what CPython already uses internally. If it matches, I don't see why we'd even bother going through the __subclasscheck__ and __instancecheck__ hooks. IMO, it should only use those (whichever ends up being the prefered choice - I have no strong preference for now either way) if the standard exception lookup fails, and possibly including the fact that BaseException doesn't need to be a direct subclass (e.g. virtual subclasses).
Just my 2 cents.
-Emanuel 		 	   		  
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