Update app.py

app.py

@@ -60,6 +60,7 @@ QUESTIONS = [
 ]
 
 QUIZ_DURATION_SECONDS = 60 * 60  # 1 hour
+DEFAULT_PROMPT = "-- Select an option --"
 
 # --- Helper functions ---
 
@@ -82,11 +83,12 @@ def prepare_quiz():
         quiz.append({"q": q["q"], "options": opts, "answer": new_answer_index})
 
     st.session_state.quiz = quiz
-    # initialize user answers (0 means not answered because we will add a placeholder at index 0 in selects)
+
+    # initialize user answers as the placeholder string so selectbox sees a valid value
     for i in range(len(quiz)):
         key = f"q{i}"
         if key not in st.session_state:
-            st.session_state[key] = 0
+            st.session_state[key] = DEFAULT_PROMPT
 
 
 def compute_results():
@@ -97,9 +99,9 @@ def compute_results():
     total = len(st.session_state.quiz)
     score = 0
     for i, q in enumerate(st.session_state.quiz):
-        sel_index = st.session_state.get(f"q{i}", 0)
-        # our select index 0 means "-- Select --"; actual options start at 1
-        if sel_index and (sel_index - 1) == q["answer"]:
+        sel_text = st.session_state.get(f"q{i}", DEFAULT_PROMPT)
+        correct_text = q["options"][q["answer"]]
+        if sel_text != DEFAULT_PROMPT and sel_text == correct_text:
             score += 1
 
     now = time.time()
@@ -142,8 +144,8 @@ with st.sidebar:
         st.write(f"Time used: {format_seconds(int(st.session_state.used_time))}")
 
     if st.button("Reset quiz"):
+        # clear quiz-related keys and restart
         for k in list(st.session_state.keys()):
-            # keep page config but clear quiz-related keys
             if k.startswith("q") or k in ["quiz", "submitted", "score", "used_time", "start_time"]:
                 del st.session_state[k]
         st.experimental_rerun()
@@ -157,9 +159,15 @@ if remaining == 0 and not st.session_state.submitted:
 st.markdown("---")
 for i, q in enumerate(st.session_state.quiz):
     st.write(f"**Question {i+1}.** {q['q']}")
-    display_options = ["-- Select an option --"] + q["options"]
-    # selectbox will store index (0..n)
-    sel = st.selectbox("", display_options, index=st.session_state.get(f"q{i}", 0), key=f"q{i}")
+    display_options = [DEFAULT_PROMPT] + q["options"]
+    # use a non-empty label for accessibility but hide it visually
+    label = f"Answer for question {i+1}"
+    # ensure the session value is one of the options (prepare_quiz ensured this, but be defensive)
+    if st.session_state.get(f"q{i}") not in display_options:
+        st.session_state[f"q{i}"] = DEFAULT_PROMPT
+
+    # store the selected option string in session_state (not an index) to avoid serialization errors
+    sel = st.selectbox(label, display_options, key=f"q{i}", label_visibility="collapsed")
     st.write("")
 
 st.markdown("---")
@@ -175,10 +183,10 @@ else:
     # Optionally show which answers were correct
     with st.expander("Review answers"):
         for i, q in enumerate(st.session_state.quiz):
-            user_sel = st.session_state.get(f"q{i}", 0)
-            user_text = "No answer" if user_sel == 0 else q["options"][user_sel - 1]
+            user_sel = st.session_state.get(f"q{i}", DEFAULT_PROMPT)
+            user_text = "No answer" if user_sel == DEFAULT_PROMPT else user_sel
             correct_text = q["options"][q["answer"]]
-            ok = "✅" if (user_sel and (user_sel - 1) == q["answer"]) else "❌"
+            ok = "✅" if (user_sel != DEFAULT_PROMPT and user_sel == correct_text) else "❌"
             st.write(f"**Q{i+1}.** {q['q']}")
             st.write(f"Your answer: {user_text} {ok}")
             st.write(f"Correct answer: {correct_text}")