[Python-Dev] PEP 409 update [was: PEP 409 - final?]

[Paul Moore]

On 3 February 2012 19:18, Yury Selivanov <yselivanov.ml at gmail.com> wrote:
> That's a bit far-fetched.  Using same level argumentation we can utilize
> even `0`.  `raise e from 0` (or `-1`), and use `0` object instead of
> Ellipsis.
>
> Anyways, if the PEP is not yet fully approved, I'm minus one on allowing
> of using anything other than Exception instance or None in 'raise from'
> statement.

I may have missed something here, but as far as I am aware, the PEP is
fundamentally only about allowing raise...from None to suppress
chaining.

There is an extremely obscure case where certain (generally library,
not end user) code might want to reinstate chaining. For that very
obscure case, the PEP suggests setting __cause__ to a sentinel value,
and Ellipsis is used rather than inventing a new singleton for such a
rare case. Purely by accident, the form "raise X from ..." will do the
same as explicitly setting __cause__, and it's not worth the effort of
testing for and rejecting this case.

This issue is so not worth arguing about, it's silly.

Paul.