py/objexcept: Make mp_obj_exception_get_value support subclassed excs.

Signed-off-by: Damien George <damien@micropython.org>

py/objexcept.c

@@ -111,6 +111,15 @@ mp_obj_t mp_alloc_emergency_exception_buf(mp_obj_t size_in) {
 #endif
 #endif  // MICROPY_ENABLE_EMERGENCY_EXCEPTION_BUF
 
+STATIC mp_obj_exception_t *get_native_exception(mp_obj_t self_in) {
+    assert(mp_obj_is_exception_instance(self_in));
+    if (mp_obj_is_native_exception_instance(self_in)) {
+        return MP_OBJ_TO_PTR(self_in);
+    } else {
+        return MP_OBJ_TO_PTR(((mp_obj_instance_t *)MP_OBJ_TO_PTR(self_in))->subobj[0]);
+    }
+}
+
 STATIC void decompress_error_text_maybe(mp_obj_exception_t *o) {
     #if MICROPY_ROM_TEXT_COMPRESSION
     if (o->args->len == 1 && mp_obj_is_type(o->args->items[0], &mp_type_str)) {
@@ -240,7 +249,7 @@ mp_obj_t mp_obj_exception_make_new(const mp_obj_type_t *type, size_t n_args, siz
 
 // Get exception "value" - that is, first argument, or None
 mp_obj_t mp_obj_exception_get_value(mp_obj_t self_in) {
-    mp_obj_exception_t *self = MP_OBJ_TO_PTR(self_in);
+    mp_obj_exception_t *self = get_native_exception(self_in);
     if (self->args->len == 0) {
         return mp_const_none;
     } else {
@@ -559,25 +568,15 @@ bool mp_obj_exception_match(mp_obj_t exc, mp_const_obj_t exc_type) {
 
 // traceback handling functions
 
-#define GET_NATIVE_EXCEPTION(self, self_in) \
-    /* make sure self_in is an exception instance */ \
-    assert(mp_obj_is_exception_instance(self_in)); \
-    mp_obj_exception_t *self; \
-    if (mp_obj_is_native_exception_instance(self_in)) { \
-        self = MP_OBJ_TO_PTR(self_in); \
-    } else { \
-        self = MP_OBJ_TO_PTR(((mp_obj_instance_t *)MP_OBJ_TO_PTR(self_in))->subobj[0]); \
-    }
-
 void mp_obj_exception_clear_traceback(mp_obj_t self_in) {
-    GET_NATIVE_EXCEPTION(self, self_in);
+    mp_obj_exception_t *self = get_native_exception(self_in);
     // just set the traceback to the null object
     // we don't want to call any memory management functions here
     self->traceback_data = NULL;
 }
 
 void mp_obj_exception_add_traceback(mp_obj_t self_in, qstr file, size_t line, qstr block) {
-    GET_NATIVE_EXCEPTION(self, self_in);
+    mp_obj_exception_t *self = get_native_exception(self_in);
 
     // append this traceback info to traceback data
     // if memory allocation fails (eg because gc is locked), just return
@@ -630,7 +629,7 @@ void mp_obj_exception_add_traceback(mp_obj_t self_in, qstr file, size_t line, qs
 }
 
 void mp_obj_exception_get_traceback(mp_obj_t self_in, size_t *n, size_t **values) {
-    GET_NATIVE_EXCEPTION(self, self_in);
+    mp_obj_exception_t *self = get_native_exception(self_in);
 
     if (self->traceback_data == NULL) {
         *n = 0;

tests/basics/subclass_native3.py

@@ -34,6 +34,26 @@ print(MyStopIteration().value)
 print(MyStopIteration(1).value)
 
 
+class Iter:
+    def __iter__(self):
+        return self
+
+    def __next__(self):
+        # This exception will stop the "yield from", with a value of 3
+        raise MyStopIteration(3)
+
+
+def gen():
+    print((yield from Iter()))
+    return 4
+
+
+try:
+    next(gen())
+except StopIteration as er:
+    print(er.args)
+
+
 class MyOSError(OSError):
     pass