At 08:00 PM 8/2/2005 +1000, Nick Coghlan wrote:
Python 2.4 Compatible Improved Exception Hierarchy v 0.1
Exception +-- ControlFlowException (new) +-- GeneratorExit (new) +-- StopIteration +-- SystemExit +-- KeyboardInterrupt (dual-inheritance new) +-- StandardError +-- KeyboardInterrupt (dual-inheritance new) +-- CriticalError (new) +-- MemoryError +-- SystemError +-- Error (new)
Couldn't we make Error a parent of StandardError, here, and then make the CriticalError subclasses dual-inherit StandardError, i.e.:
Error CriticalError MemoryError (also subclass StandardError) SystemError (also subclass StandardError) StandardError ...
In this way, we can encourage people to inherit from Error. Or maybe we should just make the primary hierarchy the way we want it to be, and only cross-link exceptions to StandardError that were previously under StandardError, i.e.:
Raisable ControlFlowException ... (cross-inherit to StandardError as needed) CriticalError ... (cross-inherit to StandardError as needed) Exception ...
This wouldn't avoid "except Exception" and bare except being problems, but at least you can catch the uncatchables and reraise them.
Hm. Maybe we should include a Reraisable base for ControlFlowException and CriticalError? Then you could do "except Reraisable: raise" as a nice way to do the right thing until Python 3.0.
It seems to me that multiple inheritance is definitely the right idea, though. That way, we can get the hierarchy we really want with only a minimum of boilerplate in pre-3.0 to make it actually work.