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

[Yury Selivanov]

On 2012-02-03, at 1:20 PM, Guido van Rossum wrote:
> Please. Let's stop this. There is no known use case to ever write
> that. We're just not putting specific measures to prevent it. Writing
> 
>>>> a = ...
> 
> Is likewise cute but not very informative. But it is valid syntax.

Well, right now you'll get TypeError if you want to raise an exception
from something that is not an exception.  'raise from None' will
loosen the check allowing None values, in the 'raise from' statement,
but that should be it.

To achieve the same effect as 'raise from ...' just do 
'e.__cause__ = ...'.

On the question of using Ellipsis instead of some new singleton like
__NoContext__: how's Ellipsis semantically related to exceptions after 
all?

-
Yury