On 22 November 2017 at 15:47, Paul Moore <p.f.moore@gmail.com> wrote:

I generally don't understand "await" in any context, so I deferred
judgement on that :-) Based on your comment that they are equally
tricky, I'd suggest we prohibit them both ;-)

Less facetiously, comprehensions are defined in the language reference
in terms of a source translation to nested loops. That description
isn't 100% precise, but nevertheless, if yield/async in a
comprehension doesn't behave like that, I'd consider it a bug. So
current behaviour (for both yield and await) is a bug, and your
proposed semantics for yield is correct.

I think there may be a small misunderstanding here. The situation is different for comprehensions and generator expressions,

let me summarize the current state:

- yield in comprehensions works "wrong" (a shorthand for not according to the docs/naive expectations, i.e. not equivalent to for loop)

- await in comprehensions works "right"

- yield in generator expressions works "wrong"

- await in generator expressions works "wrong"

After some thinking, both `yield` and `await` look quite mind bending in _generator expressions_, so maybe the right compromise strategy is:

- fix yield in comprehensions

- await in comprehensions already works

- make both `yield` and `await` a SyntaxError in generator expressions.

What do you think?

Ivan