Ah I misremembered. I was actually trying to do this

    x = [yield a for a in b]

Which yields (heh) an `Invalid Syntax` error. Thanks for the link to that PEP though - turns out the answer is that you almost always have to parenthesise it.

    x = [(yield a) for a in b]

> SyntaxError: yield inside list comprehension

Ok my original point stands.