[Python-Dev] Extended Function syntax

[Tim Peters]

[Guido]
> ...
> I think that for synchronized-like cases, even if it is known at
> compile time that it is to be part of the surrounding scope, the code
> generated will still need to use nested-scope-cells, since it will be
> invoked on a different stack frame: the "thunk processor" pushes its
> own frame on the stack, and I think you can't have something that
> executes in a frame that's not the topmost frame.  (Or can you?  I
> don't know exactly what generators can get away with.)

"resumable function" captures almost all salient aspects of the Python
generator implementation.  Generator resumption acts like a method call to
the resumer (generator_iterator.next(), whether explicit or implicit), and
yielding acts *almost* like a function return to the generator (the
generator's stack frame is popped just as for a function return; the primary
difference is just that the frame's refcount isn't decremented).

In short, the implementation is a way to get the same frame on the top of
the stack more than once; there's nothing there now to support execution in
a non-top frame.  If such were added, the biggest mystery would be what to
do when a non-top frame tries to exit.