[Python-Dev] except Exception as err, tb [was: with_traceback]

Brett Cannon brett at python.org
Fri Mar 2 21:46:22 CET 2007

On 3/2/07, Jim Jewett <jimjjewett at gmail.com> wrote:
> Guido van Rossum wrote:
> > Since this can conceivably be going on in parallel in multiple
> > threads, we really don't ever want to be sharing whatever object
> > contains the head of the chain of tracebacks since it mutates at every
> > frame bubble-up.
> So (full) exceptions can't be unitary objects.
> In theory, raising an already-instantiated instance could indicate "no
> traceback", which could make pre-cooked exceptions even lighter.
> Otherwise, there is no way to make exceptions reference their
> traceback directly.  Using a property which depends on both the
> exception and the frame asking (catching frame?  thread?) is ...
> probably worse than keeping them separate.
>     >>> except MyException as err, tb
> isn't so awful, and makes it clear that the traceback is no longer
> needed after the more typical
>     >>> except MyException as err
>     ...         # no raise statements needing a context or cause

Just because it popped in my head, I think::

 except Exception as exc with tb:

reads better.


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