py: Add MP_OBJ_STOP_ITERATION and make good use of it.

Also make consistent use of MP_OBJ_NOT_SUPPORTED and MP_OBJ_NULL.
This helps a lot in debugging and understanding of function API.

1 files changed, 1 insertions, 1 deletions

diff --git a/py/vm.c b/py/vm.c
index dbefdc32c..f14899ab4 100644
--- a/py/vm.c
+++ b/py/vm.c
@@ -623,7 +623,7 @@ unwind_jump:
                     DECODE_ULABEL; // the jump offset if iteration finishes; for labels are always forward
                     save_sp = sp;
                     obj1 = mp_iternext_allow_raise(TOP());
-                    if (obj1 == MP_OBJ_NULL) {
+                    if (obj1 == MP_OBJ_STOP_ITERATION) {
                         --sp; // pop the exhausted iterator
                         ip += unum; // jump to after for-block
                     } else {