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Wed Nov 22 11:30:27 EST 2017 · https://mail.python.org/pipermail/python-dev/2017-November/150698.html

On 22 November 2017 at 17:24, Antoine Pitrou <solipsis at pitrou.net> wrote:

> On Wed, 22 Nov 2017 17:08:14 +0100
> Ivan Levkivskyi <levkivskyi at gmail.com> wrote:
> > On 22 November 2017 at 16:56, Yury Selivanov <yselivanov.ml at gmail.com>
> > wrote:
> >
> > > On Wed, Nov 22, 2017 at 10:10 AM, Ivan Levkivskyi <
> levkivskyi at gmail.com>
> > > wrote:
> > > > On 22 November 2017 at 15:47, Paul Moore <p.f.moore at gmail.com>
> wrote:
> > > [...]
> > > I'm all for prohibiting using 'yield' expression in generator
> > > expressions or comprehensions.  The semantics is way to hard to
> > > understand and hence be of any value.
> > >
> > > Making 'await' a SyntaxError is absolutely not an option.  Async
> > > generator expressions are a shorthand syntax for defining asynchronous
> > > generators (PEP 525), and it's already being used in the wild.
> > >
> >
> > OK, makes sense, so it looks like we may have the following plan:
> >
> > - fix `yield` in comprehensions
> > - update PEP 530 and docs re generator expressions vs comprehensions
> > - make `yield` in generator expressions a SyntaxError
>
> Given a comprehension (e.g. list comprehension) is expected to work
> nominally as `constructor(generator expression)`
>

As Yury just explained, these two are not equivalent if there is an `await`
in the comprehension/generator expression.

--
Ivan
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[Python-Dev] Tricky way of of creating a generator via a comprehension expression