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

Guido van Rossum guido at python.org
Sat Nov 25 18:37:12 EST 2017

On Sat, Nov 25, 2017 at 1:05 PM, David Mertz <mertz at gnosis.cx> wrote:

> FWIW, on a side point. I use 'yield' and 'yield from' ALL THE TIME in real
> code. Probably 80% of those would be fine with yield statements, but a
> significant fraction use `gen.send()`.
> On the other hand, I have yet once to use 'await', or 'async' outside of
> pedagogical contexts. There are a whole lot of generators, including ones
> utilizing state injection, that are useful without the scaffolding of an
> event loop, in synchronous code.

Maybe you didn't realize async/await don't need an event loop? Driving an
async/await-based coroutine is just as simple as driving a yield-from-based
one (`await` does exactly the same thing as `yield from`).

But I won't argue with the usefulness of `yield [from]` in expressions.
That is not the topic of this thread.

> Of course, I never use them in comprehensions or generator expressions.
> And even after reading every post in this thread, the behavior (either
> existing or desired by some) such constructs have is murky and difficult
> for me to reason about. I strongly support deprecation or even just
> immediate SyntaxError in 3.7.

Maybe the rest of the discussion should be about deprecation vs.
SyntaxError in Python 3.7.

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