Update app.py

app.py

@@ -1,3 +1,4 @@
+# app.py
 import streamlit as st
 import pandas as pd
 import numpy as np
@@ -12,6 +13,7 @@ import io
 import base64
 import textwrap
 import time
+import os
 
 # Page configuration
 st.set_page_config(
@@ -633,7 +635,7 @@ elif menu == "Practice":
         
         with col3:
             if st.button("View Solution"):
-                st.code(challenge['solution"])
+                st.code(challenge["solution"])
 
 elif menu == "Projects":
     st.markdown("<h1 class='main-header'>🛠️ Hands-on Projects</h1>", unsafe_allow_html=True)