[Python-Dev] PEP 380 (yield from a subgenerator) comments

[Guido van Rossum]

On Sat, Mar 28, 2009 at 1:36 AM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote:
> Guido van Rossum wrote:
>
>> The new exception could either be a designated (built-in) subclass of
>> StopIteration, or not;
>
> I think it would have to not be; otherwise any existing
> code that catches StopIteration would catch the new
> exception as well without complaint.

OK.

> Using a different exception raises another question.
> Would you check whether the return value is None and
> raise an ordinary StopIteration in that case? Or would
> return with a value always raise the new exception?
I'm not sure it matters much, but let's sat the latter.

> If the latter, then 'return' and 'return None' would
> no longer be equivalent in all cases, which would be
> rather strange.

They already aren't in generators, 'return' is allowed but 'return None' isn't.

>> I think in either case a check in
>> PyIter_Next() would cover most cases
>
> If that's acceptable, then the check might as well
> be for None as the StopIteration value, and there's
> no need for a new exception.

I don't understand this.

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)