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

[Guido van Rossum]

On Fri, Feb 3, 2012 at 11:18 AM, 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 read your objection and disagree. The PEP *is* fully approved.

> On 2012-02-03, at 2:03 PM, Ethan Furman wrote:
>
>> Yury Selivanov wrote:
>>> 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?
>>
>>
>> Merrian Webster says:
>> ---------------------
>> el·lip·sis
>> noun \i-ˈlip-səs, e-\
>> plural el·lip·ses\-ˌsēz\
>> Definition of ELLIPSIS
>> 1
>> a : the omission of one or more words that are obviously understood but that must be supplied to make a construction grammatically complete
>> ---------------------
>>
>> Relation to exceptions:
>> Two places to look:  __context__ and __cause__
>> Priority?  __cause__
>> When do we check __context__?  if __cause__ is omitted (or Ellipsis)
>>
>> ~Ethan~
>
> _______________________________________________
> Python-Dev mailing list
> Python-Dev at python.org
> http://mail.python.org/mailman/listinfo/python-dev
> Unsubscribe: http://mail.python.org/mailman/options/python-dev/guido%40python.org



-- 
--Guido van Rossum (python.org/~guido)