[Python-Dev] Tricky way of of creating a generator via a comprehension expression (original) (raw)

Brett Cannon brett at python.org
Sat Nov 25 12:15:40 EST 2017

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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