Hi all

Does anybody know why it's not possible to raise Exceptions which are
types (new-style-classes). I know all standard exceptions are classic
classes, but if you make a custom exception which both inherits from a
exception class and a new-style one the it causes a type error when raised.
[color=blue][color=green][color=darkred]
>>> class b(Exception, object): pass[/color][/color][/color]
[color=blue][color=green][color=darkred]
>>> raise b[/color][/color][/color]

Traceback (most recent call last):
File "<pyshell#2>", line 1, in -toplevel-
raise b
TypeError: exceptions must be classes, instances, or strings
(deprecated), not type

This is weird, I think. Are there any issues about raising types as
exceptions that I can't think of ?


--
--------------------------------------
Ola Natvig <ola.natvig@infosense.no>
infoSense AS / development

Ola Natvig wrote:[color=blue]
> Does anybody know why it's not possible to raise Exceptions which are
> types (new-style-classes). I know all standard exceptions are classic
> classes, but if you make a custom exception which both inherits from a
> exception class and a new-style one the it causes a type error when raised.
>[color=green][color=darkred]
> >>> class b(Exception, object): pass[/color][/color][/color]

This might not help you, but have you considered just making
your old-style class *contain a reference* to an instance
of whatever new-style class you want it to contain? Then
the issue goes away.

I can't actually think of a reason to need to base an
exception on a new-style class, but perhaps you have a
good one...

-Peter

Peter Hansen wrote:[color=blue]
> Ola Natvig wrote:
>[color=green]
>> Does anybody know why it's not possible to raise Exceptions which are
>> types (new-style-classes). I know all standard exceptions are classic
>> classes, but if you make a custom exception which both inherits from a
>> exception class and a new-style one the it causes a type error when
>> raised.
>>[color=darkred]
>> >>> class b(Exception, object): pass[/color][/color]
>
>
> This might not help you, but have you considered just making
> your old-style class *contain a reference* to an instance
> of whatever new-style class you want it to contain? Then
> the issue goes away.
>
> I can't actually think of a reason to need to base an
> exception on a new-style class, but perhaps you have a
> good one...
>
> -Peter[/color]

It's quite simple to bypass the problem, it was more the reason I was
wondering about too.

--
--------------------------------------
Ola Natvig <ola.natvig@infosense.no>
infoSense AS / development

Google is your friend.
This has been discussed a lot in the past. For instance, google for the
thread,
"Exceptions as New Style Classes", there was also a PEP by Steven
Taschuk,
IIRC.

Michele Simionato