Hi Guido,
Thanks for the answer and thanks for the trick.
I figured it out your code. In that sample the yields run concurrently they
don't in parallel. What I'm really trying to do is *paralleling *the asyncs
*yielding *a tuple, but it's possible one of them will be None and in that
case It'll throw an exception: "None object has no attribute .get_async()".
How can I avoid this exception?
Thanks in advance and regards.
Saludos.
Moisés Belchín.
2013/1/30 Guido van Rossum <gu...@python.org>
> On Wed, Jan 30, 2013 at 9:00 AM, Moises Belchin <moisesbelc...@gmail.com>
> wrote:
> > Please take a look at this parallel tasklet code snippet #1.
> >
> >
> > @ndb.tasklet
> > def get_data_parallel(e):
> > usr, det = yield (e.user.get_async(),
> > MyKind.query(ancestor = e.key).fetch_async())
> > raise ndb.Return((e, usr, det))
> >
> >
> >
> > If e.user is None this raise an Exception.
> >
> >
> > I'm trying this snippet #2. However I still get Exception: "TypeError:
> > Expected Future, received <type 'NoneType'>: None"
> >
> >
> > @ndb.tasklet
> > def get_data_parallel(e):
> > usr, det = yield (e.user.get_async() if e.user else None,
> > MyKind.query(ancestor = e.key).fetch_async())
> > raise ndb.Return((e, usr, det))
> >
> >
> > How can I do something like snippet #2 ? How can I return future(None) or
> > future('')
>
> You can factor it out into two yields, one of which is optional. First
> create a future for the query that you always want to run:
>
> f = MyKind.query(ancestor = e.key).fetch_async() # No yield!
>
> Then conditionally yield the other async request:
>
> if e.user:
> usr = yield from e.user.get_async()
> else:
> usr = None
>
> Finally yield the future:
>
> det = yield f
>
> The trick is that the query will run when you yield the other operation.
>
> --
> --Guido van Rossum (python.org/~guido)
>
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