[Python-Dev] Tricky way of of creating a generator via a comprehension expression (original) (raw)
Ivan Levkivskyi levkivskyi at gmail.com
Wed Nov 22 10:10:11 EST 2017
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On 22 November 2017 at 15:47, Paul Moore <p.f.moore at 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
yieldandawaita SyntaxError in generator expressions.
What do you think?
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