> steven your generator example is exactly what I wanted to do; looks 
> like I'm upgrading to Python 3.8 for the new assignment syntax.
Sorry to have mislead you, but I don't think it will do what I thought. 
After giving it some more thought, I decided to test it (at least as 
much of it as possible). There's no local assignment here but you can 
see that the behaviour is not what I had assumed:

py> def inner():
...     yield from (1, 2)
...     return -1
...
py> def outer():
...     for x in (yield from inner()):
...             yield 100+x
...
py> for x in outer():
...     print(x)
...
1
2
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "<stdin>", line 2, in outer
TypeError: 'int' object is not iterable

In hindsight, this behaviour is logical. But I think it means that there 
is no way to do what you want using a for-loop.

> I was actually expecting the SyntaxError to be raised at runtime which 
> would be a pretty large behavior change

Not *entirely* unprecedented though, as you can get runtime SyntaxErrors 
from calling compile(), eval() or exec(). But I think some other class 
of exception would be better, since the problem isn't actually a syntax 
error.