> How about fixing CPython to raise SyntaxWarning or even SyntaxError?

I think it is better to just fix the issue, i.e. make comprehensions be equivalent to for-loops even if they contain `yield`. (In particular this will lead to [(yield i) for i in range(5)] be SyntaxError outside function).

The example of `await` shows that it is possible without leaking the loop variable into enclosing scope.