WebSocket transport not available. Install eventlet or gevent and gevent-websocket for improved performance
Normally you do not include the async_mode option when you instantiate your server. By having async_mode='threading' you are forcing the server to ignore eventlet and/or gevent and go with the more basic server, which does not support WebSocket.
So remove async_mode, then install eventlet (or gevent and gevent-websocket). Now your server will have access to WebSocket and will not show the warning.
If it's the problem occurred when executing a python fileJust try pip install eventlet its worked for me you can also try pip install gevent some times this can also do the trick!