Update app.py

app.py

@@ -19,11 +19,19 @@ TICKERS = [
 
 def optimize_portfolio(years, target_return):
     try:
-        data = yf.download(TICKERS, period=f"{years}y", interval="1mo")
-        if "Adj Close" not in data.columns:
-            return pd.DataFrame(), "Error: 'Adj Close' column missing.", "", "", ""
+        data = yf.download(TICKERS, period=f"{years}y", interval="1mo", group_by="ticker", auto_adjust=True)
+
+        if isinstance(data.columns, pd.MultiIndex):
+            try:
+                prices = pd.concat([data[ticker]['Close'] for ticker in TICKERS], axis=1)
+                prices.columns = TICKERS
+            except Exception:
+                return pd.DataFrame(), "Error: Failed to extract Close prices from multi-index data.", "", "", ""
+        else:
+            prices = data.get("Adj Close")
+            if prices is None or prices.empty:
+                return pd.DataFrame(), "Error: 'Adj Close' data not found or empty.", "", "", ""
 
-        prices = data['Adj Close']
         returns = prices.pct_change().dropna()
         mean_returns = returns.mean() * 12
         cov_matrix = returns.cov() * 12