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

[Brett Cannon]

On Fri, Nov 24, 2017, 19:32 Guido van Rossum, <guido at python.org> wrote:

> On Fri, Nov 24, 2017 at 4:22 PM, Guido van Rossum <guido at python.org>
> wrote:
>
>> The more I hear about this topic, the more I think that `await`, `yield`
>> and `yield from` should all be banned from occurring in all comprehensions
>> and generator expressions. That's not much different from disallowing
>> `return` or `break`.
>>
>
> From the responses it seems that I tried to simplify things too far. Let's
> say that `await` in comprehensions is fine, as long as that comprehension
> is contained in an `async def`. While we *could* save `yield [from]` in
> comprehensions, I still see it as mostly a source of confusion, and the
> fact that the presence of `yield [from]` *implicitly* makes the surrounding
> `def` a generator makes things worse. It just requires too many mental
> contortions to figure out what it does.
>
> I still propose to rule out all of the above from generator expressions,
> because those can escape from the surrounding scope.
>

+1 from me.

-Brett


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