On 26 January 2017 at 00:53, Nathaniel Smith <njs@pobox.com> wrote:

I'm not sure this is actually a good idea, given the potential for ambiguity and backwards compatibility considerations -- I'm kind of leaning towards the deprecate/error option on balance :-). But it's an option that would probably be less confusing than the status quo, and would make it easier to write the kind of straddling code the original poster was trying to write.

Concerning list/set/dict comprehensions, I am much more in favor of making comprehensions simply equivalent to for-loops (more or less like you proposed using yield from). The only reason to introduce auxiliary function scope was to prevent the loop variables from leaking outside comprehensions.
Formally, this is indeed backward incompatible, but I doubt many people depend on the current counter-intuitive behavior.

Concerning generator expressions, probably it is indeed better to simply prohibit yield inside them.

Ivan