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[Python-Dev] GeneratorExit inheriting from Exception

Georg Brandl g.brandl at gmx.net
Sat Mar 18 16:31:13 CET 2006 
Barry Warsaw wrote:
> On Sat, 2006-03-18 at 22:53 +1000, Nick Coghlan wrote:
>> Should GeneratorExit inherit from Exception or BaseException?
> 
> Actually, this prompts me to write about an issue I have with PEP 352.
> I actually don't think it's necessary (yes, I know it's already in the
> tree).
> 
> What I would much rather is is for StandardError to be renamed Error,
> for Exception to remain the base class of the exception hierarchy, and
> for KeyboardInterrupt to be moved to inherit directly from Exception.
> GeneratorExit, SystemExit, and StopIteration would continue to inherit
> from Exception.
> 
> The reasoning is this: anything that can be raised is an Exception.  Not
> all Exceptions are Errors.  Anything that signals an error condition is
> an Error, and anything that signals a warning condition is a Warning.
> Thus the basic hierarchy /ought/ to be:
> 
> Exception
> +- KeyboardInterrupt
> +- GeneratorExit
> +- SystemExit
> +- StopIteration
> +- Error
> |  +- ImportError
> |  +- (etc.)
> |
> +- Warning
>    +- UserWarning
>    +- (etc.)

Cool! That's so far the clearest solution. An additional bonus is that except
statements look nicer:

except:            # still catches all Exceptions, just like
except Exception:

except Error:      # is what you normally should do

Cheers,
Georg
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