At 11:43 PM 7/30/2005 +1000, Nick Coghlan wrote:
>Here's a fairly minimal proposal, which is closer to the existing 2.4
>structure:
>
>New Hierarchy
>=============
>
>Raisable (formerly Exception)
>+-- CriticalException (new)
> +-- KeyboardInterrupt
> +-- MemoryError
> +-- SystemError
>+-- ControlFlowException (new)
> +-- GeneratorExit
> +-- StopIteration
> +-- SystemExit
>+-- Exception (formerly StandardError)
> +-- AssertionError
> +-- AttributeError
> +-- ImportError
> +-- TypeError
> +-- WeakReferenceError (formerly ReferenceError)
I like this a lot, and a good bit of it could actually be done in 2.5,
apart from the Exception/StandardError move, assuming also that the renamed
errors were also available under their old names. We could probably go so
far as to add Raisable to the hierarchy, but I don't think we could
actually get quite to your proposed structure without breaking any
programs. On the other hand, if we introduce CriticalException and
ControlFlowException in 2.5 (inheriting from Exception), and create a new
Error base for StandardError, then promote subclassing and catching it
instead of Exception, then there will be less to do in 3.0. So, my
thoughts for the 2.x series are:
Exception
CriticalException
ControlFlowException
Error
StandardError
with the children of these being as you've proposed. Now, "except Error:"
would be the replacement for a bare except in most cases, and we would
recommend subclassing one of the three Exception subclasses instead of
Exception itself, maybe even introduce a PendingDeprecationWarning for
direct Exception subclasses outside the exceptions module, with a
DeprecationWarning in 2.6 and beyond.
Note that subclassing Error instead of Exception won't hurt any programs
that already catch Exception, and if they have to deal with libraries that
haven't made the move, they can always use this pattern:
except (CriticalException,ControlFlowException):
raise
except:
# whatever
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