objtype: Clarify comment for mp_obj_class_lookup().

py/objtype.c

@@ -90,13 +90,15 @@ STATIC int instance_count_native_bases(const mp_obj_type_t *type, const mp_obj_t
 // http://python-history.blogspot.com/2010/06/method-resolution-order.html
 // https://www.python.org/download/releases/2.3/mro/
 //
-// will return MP_OBJ_NULL if not found
+// will keep lookup->dest[0]'s value (should be MP_OBJ_NULL on invocation) if attribute
-// will return MP_OBJ_SENTINEL if special method was found in a native type base
+// is not found
-// via slot id (meth_offset). As there can be only one native base, it's known that it
+// will set lookup->dest[0] to MP_OBJ_SENTINEL if special method was found in a native
-// applies to instance->subobj[0]. In most cases, we also don't need to know which type
+// type base via slot id (as specified by lookup->meth_offset). As there can be only one
-// it was - because instance->subobj[0] is of that type. The only exception is when
+// native base, it's known that it applies to instance->subobj[0]. In most cases, we also
-// object is not yet constructed, then we need to know base native type to construct
+// don't need to know which type it was - because instance->subobj[0] is of that type.
-// instance->subobj[0]. This case is handled via instance_count_native_bases() though.
+// The only exception is when object is not yet constructed, then we need to know base
+// native type to construct its instance->subobj[0] from. But this case is handled via
+// instance_count_native_bases(), which returns a native base which it saw.
 struct class_lookup_data {
     mp_obj_instance_t *obj;
     qstr attr;