py: Rename MP_OBJ_NOT_SUPPORTED to MP_OBJ_NULL.

See issue #608 for justification.

18 files changed, 60 insertions, 69 deletions

diff --git a/py/obj.c b/py/obj.c
index 3617ff6761..f8b5ee34d9 100644
--- a/py/obj.c
+++ b/py/obj.c
@@ -122,7 +122,7 @@ int mp_obj_is_true(mp_obj_t arg) {
         mp_obj_type_t *type = mp_obj_get_type(arg);
         if (type->unary_op != NULL) {
             mp_obj_t result = type->unary_op(MP_UNARY_OP_BOOL, arg);
-            if (result != MP_OBJ_NOT_SUPPORTED) {
+            if (result != MP_OBJ_NULL) {
                 return result == mp_const_true;
             }
         }
@@ -212,7 +212,7 @@ bool mp_obj_equal(mp_obj_t o1, mp_obj_t o2) {
     mp_obj_type_t *type = mp_obj_get_type(o1);
     if (type->binary_op != NULL) {
         mp_obj_t r = type->binary_op(MP_BINARY_OP_EQUAL, o1, o2);
-        if (r != MP_OBJ_NOT_SUPPORTED) {
+        if (r != MP_OBJ_NULL) {
             return r == mp_const_true ? true : false;
         }
     }
@@ -357,12 +357,7 @@ mp_obj_t mp_obj_len_maybe(mp_obj_t o_in) {
     } else {
         mp_obj_type_t *type = mp_obj_get_type(o_in);
         if (type->unary_op != NULL) {
-            mp_obj_t val = type->unary_op(MP_UNARY_OP_LEN, o_in);
-            // TODO: Here's the case of having MP_OBJ_NOT_SUPPORTED is confusing
-            if (val == MP_OBJ_NOT_SUPPORTED) {
-                return MP_OBJ_NULL;
-            }
-            return val;
+            return type->unary_op(MP_UNARY_OP_LEN, o_in);
         } else {
             return MP_OBJ_NULL;
         }
@@ -373,7 +368,7 @@ mp_obj_t mp_obj_subscr(mp_obj_t base, mp_obj_t index, mp_obj_t value) {
     mp_obj_type_t *type = mp_obj_get_type(base);
     if (type->subscr != NULL) {
         mp_obj_t ret = type->subscr(base, index, value);
-        if (ret != MP_OBJ_NOT_SUPPORTED) {
+        if (ret != MP_OBJ_NULL) {
             return ret;
         }
         // TODO: call base classes here?
diff --git a/py/obj.h b/py/obj.h
index 14ced0691a..2df597de75 100644
--- a/py/obj.h
+++ b/py/obj.h
@@ -52,8 +52,7 @@ typedef struct _mp_obj_base_t mp_obj_base_t;
 // These fake objects are used to indicate certain things in arguments or return
 // values, and should only be used when explicitly allowed.
 //
-//  - MP_OBJ_NULL : used to indicate the absence of an object.
-//  - MP_OBJ_NOT_SUPPORTED : a return value that indicates an unsupported operation.
+//  - MP_OBJ_NULL : used to indicate the absence of an object, or unsupported operation.
 //  - MP_OBJ_STOP_ITERATION : used instead of throwing a StopIteration, for efficiency.
 //  - MP_OBJ_SENTINEL : used for various internal purposes where one needs
 //    an object which is unique from all other objects, including MP_OBJ_NULL.
@@ -63,14 +62,12 @@ typedef struct _mp_obj_base_t mp_obj_base_t;
 
 #if NDEBUG
 #define MP_OBJ_NULL             ((mp_obj_t)0)
-#define MP_OBJ_NOT_SUPPORTED    ((mp_obj_t)0)
 #define MP_OBJ_STOP_ITERATION   ((mp_obj_t)0)
 #define MP_OBJ_SENTINEL         ((mp_obj_t)4)
 #else
 #define MP_OBJ_NULL             ((mp_obj_t)0)
-#define MP_OBJ_NOT_SUPPORTED    ((mp_obj_t)4)
-#define MP_OBJ_STOP_ITERATION   ((mp_obj_t)8)
-#define MP_OBJ_SENTINEL         ((mp_obj_t)12)
+#define MP_OBJ_STOP_ITERATION   ((mp_obj_t)4)
+#define MP_OBJ_SENTINEL         ((mp_obj_t)8)
 #endif
 
 // These macros check for small int, qstr or object, and access small int and qstr values
@@ -256,15 +253,15 @@ struct _mp_obj_type_t {
     mp_make_new_fun_t make_new;     // to make an instance of the type
 
     mp_call_fun_t call;
-    mp_unary_op_fun_t unary_op;     // can return MP_OBJ_NOT_SUPPORTED if op not supported
-    mp_binary_op_fun_t binary_op;   // can return MP_OBJ_NOT_SUPPORTED if op not supported
+    mp_unary_op_fun_t unary_op;     // can return MP_OBJ_NULL if op not supported
+    mp_binary_op_fun_t binary_op;   // can return MP_OBJ_NULL if op not supported
 
     mp_load_attr_fun_t load_attr;
     mp_store_attr_fun_t store_attr; // if value is MP_OBJ_NULL, then delete that attribute
 
     mp_subscr_fun_t subscr;         // implements load, store, delete subscripting
                                     // value=MP_OBJ_NULL means delete, value=MP_OBJ_SENTINEL means load, else store
-                                    // can return MP_OBJ_NOT_SUPPORTED
+                                    // can return MP_OBJ_NULL if op not supported
 
     mp_fun_1_t getiter;
     mp_fun_1_t iternext; // may return MP_OBJ_STOP_ITERATION as an optimisation instead of raising StopIteration() (with no args)
@@ -483,11 +480,11 @@ typedef struct _mp_obj_float_t {
     mp_float_t value;
 } mp_obj_float_t;
 mp_float_t mp_obj_float_get(mp_obj_t self_in);
-mp_obj_t mp_obj_float_binary_op(int op, mp_float_t lhs_val, mp_obj_t rhs); // can return MP_OBJ_NOT_SUPPORTED
+mp_obj_t mp_obj_float_binary_op(int op, mp_float_t lhs_val, mp_obj_t rhs); // can return MP_OBJ_NULL if op not supported
 
 // complex
 void mp_obj_complex_get(mp_obj_t self_in, mp_float_t *real, mp_float_t *imag);
-mp_obj_t mp_obj_complex_binary_op(int op, mp_float_t lhs_real, mp_float_t lhs_imag, mp_obj_t rhs_in); // can return MP_OBJ_NOT_SUPPORTED
+mp_obj_t mp_obj_complex_binary_op(int op, mp_float_t lhs_real, mp_float_t lhs_imag, mp_obj_t rhs_in); // can return MP_OBJ_NULL if op not supported
 #endif
 
 // tuple
diff --git a/py/objarray.c b/py/objarray.c
index 81ab57139a..d973a4c563 100644
--- a/py/objarray.c
+++ b/py/objarray.c
@@ -140,7 +140,7 @@ STATIC mp_obj_t array_unary_op(int op, mp_obj_t o_in) {
     switch (op) {
         case MP_UNARY_OP_BOOL: return MP_BOOL(o->len != 0);
         case MP_UNARY_OP_LEN: return MP_OBJ_NEW_SMALL_INT(o->len);
-        default: return MP_OBJ_NOT_SUPPORTED;
+        default: return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -166,7 +166,7 @@ STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
         // TODO implement
         // TODO: confirmed that both bytearray and array.array support
         // slice deletion
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL; // op not supported
     } else {
         mp_obj_array_t *o = self_in;
         if (MP_OBJ_IS_TYPE(index_in, &mp_type_slice)) {
@@ -174,7 +174,7 @@ STATIC mp_obj_t array_subscr(mp_obj_t self_in, mp_obj_t index_in, mp_obj_t value
                 // Only getting a slice is suported so far, not assignment
                 // TODO: confirmed that both bytearray and array.array support
                 // slice assignment (incl. of different size)
-                return MP_OBJ_NOT_SUPPORTED;
+                return MP_OBJ_NULL; // op not supported
             }
             machine_uint_t start, stop;
             if (!mp_seq_get_fast_slice_indexes(o->len, index_in, &start, &stop)) {
diff --git a/py/objbool.c b/py/objbool.c
index e31e7a2a42..4fe7a19341 100644
--- a/py/objbool.c
+++ b/py/objbool.c
@@ -76,7 +76,7 @@ STATIC mp_obj_t bool_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
     if (MP_BINARY_OP_OR <= op && op <= MP_BINARY_OP_NOT_EQUAL) {
         return mp_binary_op(op, MP_OBJ_NEW_SMALL_INT((machine_int_t)mp_obj_is_true(lhs_in)), rhs_in);
     }
-    return MP_OBJ_NOT_SUPPORTED;
+    return MP_OBJ_NULL; // op not supported
 }
 
 const mp_obj_type_t mp_type_bool = {
diff --git a/py/objcomplex.c b/py/objcomplex.c
index 18e0edc519..80a13c6d8f 100644
--- a/py/objcomplex.c
+++ b/py/objcomplex.c
@@ -123,7 +123,7 @@ STATIC mp_obj_t complex_unary_op(int op, mp_obj_t o_in) {
         case MP_UNARY_OP_BOOL: return MP_BOOL(o->real != 0 || o->imag != 0);
         case MP_UNARY_OP_POSITIVE: return o_in;
         case MP_UNARY_OP_NEGATIVE: return mp_obj_new_complex(-o->real, -o->imag);
-        default: return MP_OBJ_NOT_SUPPORTED;
+        default: return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -233,7 +233,7 @@ mp_obj_t mp_obj_complex_binary_op(int op, mp_float_t lhs_real, mp_float_t lhs_im
         case MP_BINARY_OP_EQUAL: return MP_BOOL(lhs_real == rhs_real && lhs_imag == rhs_imag);
 
         default:
-            return MP_OBJ_NOT_SUPPORTED;
+            return MP_OBJ_NULL; // op not supported
     }
     return mp_obj_new_complex(lhs_real, lhs_imag);
 }
diff --git a/py/objdict.c b/py/objdict.c
index 9d4ebb6279..f41eacd939 100644
--- a/py/objdict.c
+++ b/py/objdict.c
@@ -103,7 +103,7 @@ STATIC mp_obj_t dict_unary_op(int op, mp_obj_t self_in) {
     switch (op) {
         case MP_UNARY_OP_BOOL: return MP_BOOL(self->map.used != 0);
         case MP_UNARY_OP_LEN: return MP_OBJ_NEW_SMALL_INT((machine_int_t)self->map.used);
-        default: return MP_OBJ_NOT_SUPPORTED;
+        default: return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -140,7 +140,7 @@ STATIC mp_obj_t dict_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
         }
         default:
             // op not supported
-            return MP_OBJ_NOT_SUPPORTED;
+            return MP_OBJ_NULL;
     }
 }
 
@@ -463,13 +463,13 @@ STATIC void dict_view_print(void (*print)(void *env, const char *fmt, ...), void
 }
 
 STATIC mp_obj_t dict_view_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
-    /* only supported for the 'keys' kind until sets and dicts are refactored */
+    // only supported for the 'keys' kind until sets and dicts are refactored
     mp_obj_dict_view_t *o = lhs_in;
     if (o->kind != MP_DICT_VIEW_KEYS) {
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL; // op not supported
     }
     if (op != MP_BINARY_OP_IN) {
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL; // op not supported
     }
     return dict_binary_op(op, o->dict, rhs_in);
 }
diff --git a/py/objfloat.c b/py/objfloat.c
index e27942143d..6732f31215 100644
--- a/py/objfloat.c
+++ b/py/objfloat.c
@@ -96,7 +96,7 @@ STATIC mp_obj_t float_unary_op(int op, mp_obj_t o_in) {
         case MP_UNARY_OP_BOOL: return MP_BOOL(o->value != 0);
         case MP_UNARY_OP_POSITIVE: return o_in;
         case MP_UNARY_OP_NEGATIVE: return mp_obj_new_float(-o->value);
-        default: return MP_OBJ_NOT_SUPPORTED;
+        default: return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -165,7 +165,7 @@ mp_obj_t mp_obj_float_binary_op(int op, mp_float_t lhs_val, mp_obj_t rhs_in) {
         case MP_BINARY_OP_MORE_EQUAL: return MP_BOOL(lhs_val >= rhs_val);
 
         default:
-            return MP_OBJ_NOT_SUPPORTED;
+            return MP_OBJ_NULL; // op not supported
     }
     return mp_obj_new_float(lhs_val);
 }
diff --git a/py/objfun.c b/py/objfun.c
index 27cba3abe3..26dfe0b2e2 100644
--- a/py/objfun.c
+++ b/py/objfun.c
@@ -59,7 +59,7 @@ STATIC mp_obj_t fun_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
             // we don't even need to check for 2nd arg type.
             return MP_BOOL(lhs_in == rhs_in);
     }
-    return MP_OBJ_NOT_SUPPORTED;
+    return MP_OBJ_NULL; // op not supported
 }
 
 STATIC mp_obj_t fun_native_call(mp_obj_t self_in, uint n_args, uint n_kw, const mp_obj_t *args) {
diff --git a/py/objint.c b/py/objint.c
index 3aaf5107c4..a3b3554008 100644
--- a/py/objint.c
+++ b/py/objint.c
@@ -216,7 +216,7 @@ bool mp_obj_int_is_positive(mp_obj_t self_in) {
 
 // This is called for operations on SMALL_INT that are not handled by mp_unary_op
 mp_obj_t mp_obj_int_unary_op(int op, mp_obj_t o_in) {
-    return MP_OBJ_NOT_SUPPORTED;
+    return MP_OBJ_NULL; // op not supported
 }
 
 // This is called for operations on SMALL_INT that are not handled by mp_binary_op
@@ -285,7 +285,7 @@ mp_obj_t mp_obj_int_binary_op_extra_cases(int op, mp_obj_t lhs_in, mp_obj_t rhs_
             return mp_binary_op(op, rhs_in, lhs_in);
         }
     }
-    return MP_OBJ_NOT_SUPPORTED;
+    return MP_OBJ_NULL; // op not supported
 }
 
 // this is a classmethod
diff --git a/py/objint_longlong.c b/py/objint_longlong.c
index a9aea39312..1e0167b464 100644
--- a/py/objint_longlong.c
+++ b/py/objint_longlong.c
@@ -64,7 +64,7 @@ mp_obj_t mp_obj_int_unary_op(int op, mp_obj_t o_in) {
         case MP_UNARY_OP_POSITIVE: return o_in;
         case MP_UNARY_OP_NEGATIVE: return mp_obj_new_int_from_ll(-o->val);
         case MP_UNARY_OP_INVERT: return mp_obj_new_int_from_ll(~o->val);
-        default: return MP_OBJ_NOT_SUPPORTED;
+        default: return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -77,7 +77,7 @@ mp_obj_t mp_obj_int_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
     } else if (MP_OBJ_IS_TYPE(lhs_in, &mp_type_int)) {
         lhs_val = ((mp_obj_int_t*)lhs_in)->val;
     } else {
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL; // op not supported
     }
 
     if (MP_OBJ_IS_SMALL_INT(rhs_in)) {
@@ -135,7 +135,7 @@ mp_obj_t mp_obj_int_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
             return MP_BOOL(lhs_val == rhs_val);
 
         default:
-            return MP_OBJ_NOT_SUPPORTED;
+            return MP_OBJ_NULL; // op not supported
     }
 }
 
diff --git a/py/objint_mpz.c b/py/objint_mpz.c
index 32c8595f53..2df3232e9c 100644
--- a/py/objint_mpz.c
+++ b/py/objint_mpz.c
@@ -90,7 +90,7 @@ mp_obj_t mp_obj_int_unary_op(int op, mp_obj_t o_in) {
         case MP_UNARY_OP_POSITIVE: return o_in;
         case MP_UNARY_OP_NEGATIVE: { mp_obj_int_t *o2 = mp_obj_int_new_mpz(); mpz_neg_inpl(&o2->mpz, &o->mpz); return o2; }
         case MP_UNARY_OP_INVERT: { mp_obj_int_t *o2 = mp_obj_int_new_mpz(); mpz_not_inpl(&o2->mpz, &o->mpz); return o2; }
-        default: return MP_OBJ_NOT_SUPPORTED;
+        default: return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -108,7 +108,7 @@ mp_obj_t mp_obj_int_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
         zlhs = &((mp_obj_int_t*)lhs_in)->mpz;
     } else {
         // unsupported type
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL;
     }
 
     // if rhs is small int, then lhs was not (otherwise mp_binary_op handles it)
@@ -213,7 +213,7 @@ mp_obj_t mp_obj_int_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
                 break;
 
             default:
-                return MP_OBJ_NOT_SUPPORTED;
+                return MP_OBJ_NULL; // op not supported
         }
 
         return res;
@@ -233,7 +233,7 @@ mp_obj_t mp_obj_int_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
                 return MP_BOOL(cmp == 0);
 
             default:
-                return MP_OBJ_NOT_SUPPORTED;
+                return MP_OBJ_NULL; // op not supported
         }
     }
 }
diff --git a/py/objlist.c b/py/objlist.c
index 0ef685daeb..ee74926923 100644
--- a/py/objlist.c
+++ b/py/objlist.c
@@ -103,7 +103,7 @@ STATIC mp_obj_t list_unary_op(int op, mp_obj_t self_in) {
     switch (op) {
         case MP_UNARY_OP_BOOL: return MP_BOOL(self->len != 0);
         case MP_UNARY_OP_LEN: return MP_OBJ_NEW_SMALL_INT(self->len);
-        default: return MP_OBJ_NOT_SUPPORTED;
+        default: return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -112,7 +112,7 @@ STATIC mp_obj_t list_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
     switch (op) {
         case MP_BINARY_OP_ADD: {
             if (!MP_OBJ_IS_TYPE(rhs, &mp_type_list)) {
-                return MP_OBJ_NOT_SUPPORTED;
+                return MP_OBJ_NULL; // op not supported
             }
             mp_obj_list_t *p = rhs;
             mp_obj_list_t *s = list_new(o->len + p->len);
@@ -121,7 +121,7 @@ STATIC mp_obj_t list_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
         }
         case MP_BINARY_OP_INPLACE_ADD: {
             if (!MP_OBJ_IS_TYPE(rhs, &mp_type_list)) {
-                return MP_OBJ_NOT_SUPPORTED;
+                return MP_OBJ_NULL; // op not supported
             }
             list_extend(lhs, rhs);
             return o;
@@ -129,7 +129,7 @@ STATIC mp_obj_t list_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
         case MP_BINARY_OP_MULTIPLY: {
             machine_int_t n;
             if (!mp_obj_get_int_maybe(rhs, &n)) {
-                return MP_OBJ_NOT_SUPPORTED;
+                return MP_OBJ_NULL; // op not supported
             }
             mp_obj_list_t *s = list_new(o->len * n);
             mp_seq_multiply(o->items, sizeof(*o->items), o->len, n, s->items);
@@ -143,7 +143,7 @@ STATIC mp_obj_t list_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
             return MP_BOOL(list_cmp_helper(op, lhs, rhs));
 
         default:
-            return MP_OBJ_NOT_SUPPORTED;
+            return MP_OBJ_NULL; // op not supported
     }
 }
 
diff --git a/py/objnone.c b/py/objnone.c
index bb4e7e5608..165c8e5a43 100644
--- a/py/objnone.c
+++ b/py/objnone.c
@@ -44,7 +44,7 @@ STATIC void none_print(void (*print)(void *env, const char *fmt, ...), void *env
 STATIC mp_obj_t none_unary_op(int op, mp_obj_t o_in) {
     switch (op) {
         case MP_UNARY_OP_BOOL: return mp_const_false;
-        default: return MP_OBJ_NOT_SUPPORTED;
+        default: return MP_OBJ_NULL; // op not supported
     }
 }
 
diff --git a/py/objset.c b/py/objset.c
index a6f1fe7339..32c194db12 100644
--- a/py/objset.c
+++ b/py/objset.c
@@ -475,7 +475,7 @@ STATIC mp_obj_t set_unary_op(int op, mp_obj_t self_in) {
     switch (op) {
         case MP_UNARY_OP_BOOL: return MP_BOOL(self->set.used != 0);
         case MP_UNARY_OP_LEN: return MP_OBJ_NEW_SMALL_INT((machine_int_t)self->set.used);
-        default: return MP_OBJ_NOT_SUPPORTED;
+        default: return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -514,7 +514,7 @@ STATIC mp_obj_t set_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
             return MP_BOOL(elem != NULL);
         }
         default:
-            return MP_OBJ_NOT_SUPPORTED;
+            return MP_OBJ_NULL; // op not supported
     }
 }
 
diff --git a/py/objstr.c b/py/objstr.c
index dcf4de82de..61fda12a3f 100644
--- a/py/objstr.c
+++ b/py/objstr.c
@@ -296,7 +296,7 @@ STATIC mp_obj_t str_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
 
         case MP_BINARY_OP_MULTIPLY: {
             if (!MP_OBJ_IS_SMALL_INT(rhs_in)) {
-                return MP_OBJ_NOT_SUPPORTED;
+                return MP_OBJ_NULL; // op not supported
             }
             int n = MP_OBJ_SMALL_INT_VALUE(rhs_in);
             byte *data;
@@ -341,7 +341,7 @@ uncomparable:
             }
     }
 
-    return MP_OBJ_NOT_SUPPORTED;
+    return MP_OBJ_NULL; // op not supported
 }
 
 STATIC mp_obj_t str_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
@@ -365,7 +365,7 @@ STATIC mp_obj_t str_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
             return mp_obj_new_str(self_data + index_val, 1, true);
         }
     } else {
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL; // op not supported
     }
 }
 
diff --git a/py/objtuple.c b/py/objtuple.c
index 44ee95dd96..46515378f0 100644
--- a/py/objtuple.c
+++ b/py/objtuple.c
@@ -120,7 +120,7 @@ mp_obj_t mp_obj_tuple_unary_op(int op, mp_obj_t self_in) {
     switch (op) {
         case MP_UNARY_OP_BOOL: return MP_BOOL(self->len != 0);
         case MP_UNARY_OP_LEN: return MP_OBJ_NEW_SMALL_INT(self->len);
-        default: return MP_OBJ_NOT_SUPPORTED;
+        default: return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -129,7 +129,7 @@ mp_obj_t mp_obj_tuple_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
     switch (op) {
         case MP_BINARY_OP_ADD: {
             if (!mp_obj_is_subclass_fast(mp_obj_get_type(rhs), (mp_obj_t)&mp_type_tuple)) {
-                return MP_OBJ_NOT_SUPPORTED;
+                return MP_OBJ_NULL; // op not supported
             }
             mp_obj_tuple_t *p = rhs;
             mp_obj_tuple_t *s = mp_obj_new_tuple(o->len + p->len, NULL);
@@ -138,7 +138,7 @@ mp_obj_t mp_obj_tuple_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
         }
         case MP_BINARY_OP_MULTIPLY: {
             if (!MP_OBJ_IS_SMALL_INT(rhs)) {
-                return MP_OBJ_NOT_SUPPORTED;
+                return MP_OBJ_NULL; // op not supported
             }
             int n = MP_OBJ_SMALL_INT_VALUE(rhs);
             mp_obj_tuple_t *s = mp_obj_new_tuple(o->len * n, NULL);
@@ -153,8 +153,7 @@ mp_obj_t mp_obj_tuple_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
             return MP_BOOL(tuple_cmp_helper(op, lhs, rhs));
 
         default:
-            // op not supported
-            return MP_OBJ_NOT_SUPPORTED;
+            return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -176,7 +175,7 @@ mp_obj_t mp_obj_tuple_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value) {
         uint index_value = mp_get_index(self->base.type, self->len, index, false);
         return self->items[index_value];
     } else {
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL; // op not supported
     }
 }
 
diff --git a/py/objtype.c b/py/objtype.c
index d099e3a45a..2e1c56416e 100644
--- a/py/objtype.c
+++ b/py/objtype.c
@@ -287,7 +287,7 @@ STATIC mp_obj_t instance_unary_op(int op, mp_obj_t self_in) {
     qstr op_name = unary_op_method_name[op];
     /* Still try to lookup native slot
     if (op_name == 0) {
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL;
     }
     */
     mp_obj_t member[2] = {MP_OBJ_NULL};
@@ -297,7 +297,7 @@ STATIC mp_obj_t instance_unary_op(int op, mp_obj_t self_in) {
     } else if (member[0] != MP_OBJ_NULL) {
         return mp_call_function_1(member[0], self_in);
     } else {
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -374,7 +374,7 @@ STATIC mp_obj_t instance_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
     qstr op_name = binary_op_method_name[op];
     /* Still try to lookup native slot
     if (op_name == 0) {
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL;
     }
     */
     mp_obj_t dest[3] = {MP_OBJ_NULL};
@@ -385,7 +385,7 @@ STATIC mp_obj_t instance_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
         dest[2] = rhs_in;
         return mp_call_method_n_kw(1, 0, dest);
     } else {
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -499,7 +499,7 @@ STATIC mp_obj_t instance_subscr(mp_obj_t self_in, mp_obj_t index, mp_obj_t value
             return mp_const_none;
         }
     } else {
-        return MP_OBJ_NOT_SUPPORTED;
+        return MP_OBJ_NULL; // op not supported
     }
 }
 
@@ -632,7 +632,7 @@ STATIC mp_obj_t type_binary_op(int op, mp_obj_t lhs_in, mp_obj_t rhs_in) {
             return MP_BOOL(lhs_in == rhs_in);
 
         default:
-            return MP_OBJ_NOT_SUPPORTED;
+            return MP_OBJ_NULL; // op not supported
     }
 }
 
diff --git a/py/runtime.c b/py/runtime.c
index 7c89ec4e2e..ea75280ce4 100644
--- a/py/runtime.c
+++ b/py/runtime.c
@@ -200,7 +200,7 @@ mp_obj_t mp_unary_op(int op, mp_obj_t arg) {
         mp_obj_type_t *type = mp_obj_get_type(arg);
         if (type->unary_op != NULL) {
             mp_obj_t result = type->unary_op(op, arg);
-            if (result != MP_OBJ_NOT_SUPPORTED) {
+            if (result != MP_OBJ_NULL) {
                 return result;
             }
         }
@@ -439,7 +439,7 @@ mp_obj_t mp_binary_op(int op, mp_obj_t lhs, mp_obj_t rhs) {
         mp_obj_type_t *type = mp_obj_get_type(rhs);
         if (type->binary_op != NULL) {
             mp_obj_t res = type->binary_op(op, rhs, lhs);
-            if (res != MP_OBJ_NOT_SUPPORTED) {
+            if (res != MP_OBJ_NULL) {
                 return res;
             }
         }
@@ -467,7 +467,7 @@ generic_binary_op:
     type = mp_obj_get_type(lhs);
     if (type->binary_op != NULL) {
         mp_obj_t result = type->binary_op(op, lhs, rhs);
-        if (result != MP_OBJ_NOT_SUPPORTED) {
+        if (result != MP_OBJ_NULL) {
             return result;
         }
     }