With apologies for not reading the PEP or this thread in full, some comments: - I really like the syntax "except <exc> [as <var>] [if <test>]:". This addresses a pretty common use case in my experience. I don't care for the alternate proposed syntax that started this thread. I'm not sure that the 'if' subclause makes sense without the 'as' subclause, since most likely you'd want to refer to the caught exception. I note that it is more powerful than putting "if not <test>: raise" in the body of the except-clause, because it will allow subsequent except clauses to match still. I also note that it is a much "cleaner" change than (again) reorganizing the exception hierarchy, since there is no backward compatibility to consider. - Regarding restructuring the exception tree, I don't think this needs to wait for Python 4. (We've done it several times during Python 2.) But it is very tricky to do it without breaking existing code, and I'm not sure that deprecations will help that much. E.g. if two exceptions A and B are currently not related via inheritance, and we were to make A a subclass of B, then in code of the form try: ... except B: ... except A: ... the except A clause would become unreachable. Maybe it's easier to propose small changes instead of trying to refactor a huge section of the exception tree? - Quite independently, I think it is time that we started documenting which exceptions are raised from standard APIs. The trick is to avoid overdocumenting: there is no point in documenting that everything can raise MemoryError or that passing in wildly invalid arguments can raise TypeError or AttributeError (and pretty much anything else). But the variety of exceptions that may be raised by something like urlopen, depending on which layer of the network and I/O stacks detects a problem are worth documenting. Maybe this example could even be a starting point for a rationalization of some of the exceptions involved. (And if we find there are legitimate situations where a networking or I/O problem raises a "generic" error such as TypeError or AttributeError, those are probably bugs that should be fixed in the code.) - Lastly, there is a bunch of standard exception types that are usually caused by bad code (as opposed to bad data or an environmental problem). This would include NameError, TypeError, AttributeError, but not KeyError, IndexError, ValueError. Perhaps it makes sense to introduce a common base class for these "bad code" exceptions? Unlike the other exception types, I think that the set of "bad code" exceptions is pretty much static; a new library module is not going to define raise a new kind of "bad code" exception. (But it may well define a new kind of "bad data" exception, and I don't think we need a common base class for all "bad data" or "bad state" exceptions.) -- --Guido van Rossum (python.org/~guido)