correctly autodetect asgi async mode

miguelgrinberg · miguelgrinberg · commit eecd3676c15b · 2019-06-29T12:45:16.000+01:00
diff --git a/socketio/tornado.py b/socketio/tornado.py
@@ -4,8 +4,7 @@
         from engineio.async_drivers.tornado import get_tornado_handler as \
             get_engineio_handler
     except ImportError:  # pragma: no cover
-        from engineio.async_tornado import get_tornado_handler as \
-            get_engineio_handler
+        get_engineio_handler = None
 
 
 def get_tornado_handler(socketio_server):  # pragma: no cover
