Update app.py

app.py

@@ -19,11 +19,14 @@ def fetch_ohlcv_data(symbol, timeframe, limit):
     start_time = None
     while len(data) < limit:
         ohlcv_data = exchange.fetch_ohlcv(symbol, timeframe, since=start_time, limit=limit)
-        data.extend(ohlcv_data)
-        start_time = ohlcv_data[-1][0] + 1
+        if ohlcv_data:
+            data.extend(ohlcv_data)
+            start_time = ohlcv_data[-1][0] + 1
+        else:
+            print("Warning: No data returned from exchange API")
+            break
     return data
 
-
 def data_to_dataframe(data):
     df = pd.DataFrame(data, columns=['timestamp', 'open', 'high', 'low', 'close', 'volume'])
     df['timestamp'] = pd.to_datetime(df['timestamp'], unit='ms')