New style classes as exceptions (Was: exception handing)

[Jonathan Hogg]

On 1/7/2002 14:57, in article
mailman.1025531942.11729.python-list at python.org, "Mark McEahern"
<marklists at mceahern.com> wrote:

>> New style classes don't work when used as exceptions.  I guess it
>> should be considered as a bug.
> 
> Just out of curiousity:  How come you aren't subclassing from Exception?

The language doesn't require anyone to. You can throw an instance of any old
class:

>>>> class Foo: pass
> ... 
>>>> raise Foo()
> Traceback (most recent call last):
> File "<stdin>", line 1, in ?
> __main__.Foo: <__main__.Foo instance at 0x3f7aa8>
>>>> 

Besides which, it doesn't work even if you do:

>>> class FooError( StandardError, object ):
...     pass
... 
>>> raise FooError()
Traceback (most recent call last):
  File "<stdin>", line 1, in ?
TypeError: exceptions must be strings, classes, or instances, not FooError
>>> 

The problem is that only pure instances of old-style classes can be thrown.
This bit me too when I was doing the above - mixing in a new-style class
with an exception.

I'd consider this a bug too, but I haven't bothered checking Sourceforge to
see if anyone else has already.

Jonathan