source/pie_selection.py

@@ -276,16 +276,27 @@ class OBJECT_OT_select_symmetry_object(Operator, ObjectSelectOperatorMixin):
     bl_label = "Select Opposite Object"
     bl_options = {'REGISTER', 'UNDO'}
 
+    @classmethod
+    def poll(cls, context):
+        scene_obs = context.scene.objects
+        sel_obs = context.selected_objects[:]
+        active_obj = context.active_object
+        flipped_objs = [scene_obs.get(flip_name(ob.name)) for ob in sel_obs]
+        flipped_active = scene_obs.get(flip_name(active_obj.name))
+        if not (flipped_active or any(flipped_objs)):
+            cls.poll_message_set("No selected objects with corresponding opposite objects.")
+            return False
+        return True
+
     def execute(self, context):
-        objs = context.selected_objects[:]
+        scene_obs = context.scene.objects
+        sel_obs = context.selected_objects[:]
         active_obj = context.active_object
 
-        flipped_objs = [context.scene.objects.get(flip_name(ob.name)) for ob in objs]
-        flipped_active = context.scene.objects.get(flip_name(active_obj.name))
+        flipped_objs = [scene_obs.get(flip_name(ob.name)) for ob in sel_obs]
+        flipped_active = scene_obs.get(flip_name(active_obj.name))
 
-        notflipped = len(
-            [objs[i] for i in range(len(objs)) if objs[i] == flipped_objs[i]]
-        )
+        notflipped = sum([flipped_obj in (obj, None) for obj, flipped_obj in zip(sel_obs, flipped_objs)])
         if notflipped > 0:
             self.report({'WARNING'}, f"{notflipped} objects had no opposite.")