What are you trying to accomplish that needs an abstract base class?

APIError is not an Exception class, it is a meta-class, and thus it does not match the exception because it is not a *base* class of DriverError (it is DiverError's *meta* class).

Now, it is an interesting question whether we want the try/except statement's behavior to match issubclass, since intuitively we think the except in try except is doing the equivalent of issubclass (it isn't).

I don't know why this works in python2, but the class/meta-class machinery did undergo some significant changes.  So, it is possible that this is in fact a bug (ie: an unintentional change in semantics).  If so, it is also a doc bug, since the try statement docs clear say the expression must evaluate to a base class, and the virtual class (abc) docs *only* mention issubclass and isinstance.