Change the semantics of "return" in generators, as discussed on the

Iterators list and Python-Dev; e.g., these all pass now:

def g1():
    try:
        return
    except:
        yield 1
assert list(g1()) == []

def g2():
    try:
        return
    finally:
        yield 1
assert list(g2()) == [1]

def g3():
    for i in range(3):
        yield None
    yield None
assert list(g3()) == [None] * 4

compile.c:  compile_funcdef and com_return_stmt:  Just van Rossum's patch
to compile the same code for "return" regardless of function type (this
goes back to the previous scheme of returning Py_None).

ceval.c:  gen_iternext:  take a return (but not a yield) of Py_None as
meaning the generator is exhausted.

Python/ceval.c

@@ -166,6 +166,13 @@ gen_iternext(genobject *gen)
 	Py_XDECREF(f->f_back);
 	f->f_back = NULL;
 
+	/* If the generator just returned (as opposed to yielding), signal
+	 * that the generator is exhausted. */
+	if (result == Py_None && f->f_stacktop == NULL) {
+		Py_DECREF(result);
+		result = NULL;
+	}
+
 	return result;
 }