Update app.py

app.py

@@ -145,7 +145,12 @@ with gr.Blocks(title="AI Textbook Tutor") as app:
             return gr.update(choices=list(class_subject_chapters[selected_class].keys()), value=None)
 
         def update_chapters(selected_class, selected_subject):
-            return gr.update(choices=class_subject_chapters[selected_class][selected_subject], value=None)
+            try:
+                chapters = class_subject_chapters[selected_class][selected_subject]
+                return gr.update(choices=chapters, value=None)
+            except Exception as e:
+                return gr.update(choices=[], value="Error")
+
 
         def toggle_ui(selected_mode):
             if selected_mode == "File Upload Mode":