[Python-ideas] The async API of the future: yield-from

[Guido van Rossum]

On Sun, Oct 14, 2012 at 12:38 PM, Terry Reedy <tjreedy at udel.edu> wrote:
> On 10/14/2012 1:42 PM, Guido van Rossum wrote:
>> On Sun, Oct 14, 2012 at 10:27 AM, Terry Reedy <tjreedy at udel.edu> wrote:
>>> On 10/14/2012 10:36 AM, Guido van Rossum wrote:
>>>> Of course there's the question of what to do when one of the tasks
>>>> raises an error -- I haven't quite figured that out in NDB either, it
>>>> runs all the tasks to completion but the caller only sees the first
>>>> exception. I briefly considered having an "multi-exception" but it
>>>> felt too weird -- though I'm not married to that decision.
>
>>> One answer is to append the exception object to results and let the
>>> requesting code sort out what to do.
>>>
>>>
>>> def par(*args):
>>>     results = []
>>>     for task in args:
>>>        try:
>>>
>>>           result = yield from task
>>>           results.append(result)
>>>        except Exception as exc:
>>>           results.append(exc)
>>>     return results
>>
>> But then the caller would have to sort through the results and check
>> for exceptions. I want the caller to be able to use try/except as
>> well.
>
> OK. Then ...
>
>   def par(*args):
>      results = []
>      exceptions = False
>      for task in args:
>         try:
>            result = yield from task
>            results.append(result)
>         except Exception as exc:
>            results.append(exc)
>            exceptions = True
>      if not exceptions:
>         return results
>      else:
>         exc = MultiXException()
>         exc.results = results
>         raise exc
>
> Is this is what you meant by 'multi-exception'?

Yes.

> caller:
>
> try:
>    results = <whatever>
>    <process results, perhaps by iterating thru them, knowing all represent
> successed>
> except MultiXException as exc:
>    errprocess(exc.results)

In NDB I have yet to encounter a situation where I care.

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