I'm still not sure whether we should enable this optimization or not.

I haven't ever seen this pattern used in any Python code I worked with, so I suspect it's quite a rare hack.  Giving it a fast-path would give this pattern extra visibility and might encourage people to use it.

And the pattern itself... Well, it's quite ugly and barely readable.  IMO it's way better to simply rewrite such comprehension to an equivalent 'for' statement.

So I guess I'm -0 on this change.  I suggest to ask Guido on the mailing list if he agrees that this language patten is worth optimizing/promoting.