[Python-Dev] Compilation of "except FooExc as var" adds useless store

Chris Angelico rosuav at gmail.com
Sun Jan 6 10:35:37 EST 2019

On Mon, Jan 7, 2019 at 2:27 AM Serhiy Storchaka <storchaka at gmail.com> wrote:
> > The "store None" behavior can be traced down to introduction of the
> > "del except target var" behavior back in 2007:
> > https://github.com/python/cpython/commit/b940e113bf90ff71b0ef57414ea2beea9d2a4bc0#diff-cb296cc5109f5640ff3f6d7198a6abeeR1999
> >
> > There's no clear explanation why it's done like that, so probably an
> > artifact of the initial implementation. Note that even
> > https://github.com/python/cpython/commit/520b7ae27e39d1c77ea74ccd1b184d7cb43f9dcb
> > which did quite a bunch of refactoring to "except" implementation, and
> > reformatted this code, otherwise left it in place.
> Because there is a reason for such code.

What reason though??

> See issue1631942 [1] and the thread with the subject "self-contained
> exceptions" on the Python-3000 mailing list [2] for the rationale.
> In short, the code
>      try:
>          1/0
>      except Exception as e:
>          del e
> should work.

But obviously not, because the code was specifically written to set it
to None first. It's not the sort of thing that can be done
accidentally, is it?


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