[Python-Dev] Re: Exceptional inheritance patterns

[Michael Hudson]

Holger Krekel <pyth at devel.trillke.net> writes:

> Greg Ewing wrote:
>> > My point is that I like to regard try/except as a mechanism for
>> > "out-of-band" objects.  Guidos "should be shot" seems to indicate he
>> > sees try/except only useful/applicable to exception-handling.
>> 
>> If the root exception class were called something else,
>> such as 'Raisable', would that make you feel better?
>
> Yes, I certainly wouldn't object. I guess this would mean 'Exception'
> would derive from Raisable because Exception itself should probably not
> go away.  Hey, strings could inherit from Raisable, too! Just kidding :-) 

I would like an exception class that almost exceptions except
KeyboardInterrupt, SystemExit and -- maybe -- RuntimeError and
MemoryError inherited from.

except ExceptionsButThoseNastyOnesIDontWantToCatch:
    pass

? <wink>

> Then again, i think Python has a tradition of not requiring inheritance 
> but just behaviour.  And doesn't this whole issue only exist because 
> "raise X" with X being a class and autoinstantiated is allowed? 

I would say that it's more because it's useful to organize exceptional
conditions in a tree like hierarchy and inheritance is a usable way to
do this.  The fact that arranging things into tree like hierarchies
*isn't* what inheritance is usually used for in Python (unlike many
other languages) is what creates the dissonance, IMHO.

> Well, anyway, let's not add too much to the current python-dev traffic 
> with this issue.  I think it has been brought up a couple of times
> already. 

Indeed, I think someone said what I just said above in this thread
already :-)

> Hey, i have an idea: why not create a python-syntax mailing list 
> (or python-hell :-) ? 

I think I've suggested that before :-)

Today is the first day I remember where there are more new messages
waiting for me in python-dev than comp.lang.python!

Cheers,
mwh

-- 
  "The future" has arrived but they forgot to update the docs.
                                        -- R. David Murray, 9 May 2000