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Re: [Q] is 'yield from' syntax sugar for 'for'+'yield'?

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  Re: [Q] is 'yield from' syntax sugar for 'for'+'yield'? Makoto Kuwata <kwatch@gmail.com> - 2014-08-14 18:59 +0900
    Re: [Q] is 'yield from' syntax sugar for 'for'+'yield'? Marko Rauhamaa <marko@pacujo.net> - 2014-08-14 13:32 +0300

#76290 — Re: [Q] is 'yield from' syntax sugar for 'for'+'yield'?

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On Thu, Aug 14, 2014 at 6:38 PM, Chris Angelico <rosuav@gmail.com> wrote:

> On Thu, Aug 14, 2014 at 7:35 PM, Makoto Kuwata <kwatch@gmail.com> wrote:
> > I understand that::
> >
> >     yield from xs
> >
> > is syntax suger of::
> >
> >     for x in xs:
> >       yield x
>
> Not just. It's like that for simple cases, but there are edge cases
> that are much more complicated to do manually, and are simply taken
> care of. Best would be to read the PEP itself:
>
> http://www.python.org/dev/peps/pep-0380/
>
> ChrisA
>

Thank you. It seems too complicated...
I understand that 'val = yield from xs' is completely different from::

   for x in xs:
      ret = yield x
   val = x

Return value is propagated by StopIteration, like:

   it = iter(xs)
   try:
     while 1:
       yield next(it)
   except StopIteration as ex:
     val = ex.value


Thanks.

--
regards,
kwatch

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#76292

Makoto Kuwata <kwatch@gmail.com>:

> Thank you. It seems too complicated...

I recommend you stop trying to associate the "old" yield with the "new"
yield.

Asyncio coroutines "abuse" "yield from" for a specific effect. The
classic purpose of "yield" was to spoonfeed a sequence of return values
to the caller. The coroutine meaning of "yield from" has nothing
whatsoever to do about delivering computation results; instead, it
denotes a state where a blocking operation is waited for and the control
is handed off to other activities.



Marko

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