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

[Guido van Rossum]

On Wed, Oct 17, 2012 at 5:27 AM, Christian Tismer <tismer at stackless.com> wrote:
> On 17.10.12 12:38, Greg Ewing wrote:
>>
>> Guido van Rossum wrote:
>>>
>>> On Tue, Oct 16, 2012 at 2:14 PM, Greg Ewing <greg.ewing at canterbury.ac.nz>
>>> wrote:
>>>
>>>> The important idea is that just because you spawn a task, it
>>>> doesn't necessarily follow that you want to be regarded as the
>>>> *parent* of that task and receive its exceptions.
>>>
>>>
>>> Maybe. But the opposite doesn't follow either. It's a toss-up between
>>> the spawner and the waiter.
>>
>>
>> So maybe spawn() should have an option indicating that the
>> spawning task is to receive exceptions occuring in the
>> spawned task.
>>
>
> No idea if that helps here, but the same problem occurred for us
> as well. It is not always clear if an exception should be handled
> in a certain context, or if it should be passed on and get raised
> later in the context that is concerned.
>
> For that, Stackless has introduced a _bomb_ object that encapsulates
> an exception, in order to let it pass through the normal call/yield/return
> interface. It is used to send an exception over a channel, which
> will explode (raise that exception) when the receiver picks it later up.

Hmm... That sounds a little like your iriginal design for the channel
only supported transferring values. At least for NDB, all channels
support exceptions and tracebacks as an explicit alternative to the
value.

> I could think of something similar as a way to collect very many
> results in a join construct that collects everything without the need
> to handle each exception in the very moment it was raised.
>
> That would make it possible to collect results efficiently using 'yield
> from' and inspect the results later.
>
> Probably nothing new, just mentioned an idea...

I do think we're hashing out important ideas...

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