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

[Yury Selivanov]

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.

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~