[Python-Dev] with_traceback

[Collin Winter]

On 2/26/07, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
> Phillip J. Eby wrote:
> > At 03:38 PM 2/26/2007 -0700, Andrew Dalke wrote:
> >
> > > NO_END_OF_RECORD = ParserError("Cannot find end of record")
> >
> > Then don't do that, as it's bad style for Python 3.x.  ;-)
>
> I don't like that answer. I can think of legitimate
> reasons for wanting to pre-create exceptions, e.g. if
> I'm intending to raise and catch a particular exception
> frequently and I don't want the overhead of creating
> a new instance each time.

Is this really the problem it's being made out to be? I'm guessing the
use-case you're suggesting is where certain exceptions are raised and
caught inside a library or application, places where the exceptions
will never reach the user. If that's the case, does it really matter
what the traceback looks like?

> For me, this is casting serious doubt on the whole
> idea of attaching the traceback to the exception.

If attaching the traceback to the exception is bothering you, you
should take a look at the other attributes PEP 344 introduces:
__cause__ and __context__. I'd say what needs another look is the idea
of pre-creating a single exception instance and repeatedly raising it.

Collin Winter