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

[Ethan Furman]

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~