SimpleClient: type mismatch for SimpleClient.transport()

src/socketio/simple_client.py

@@ -103,7 +103,7 @@ class SimpleClient:
         The transport is returned as a string and can be one of ``polling``
         and ``websocket``.
         """
-        return self.client.transport if self.client else ''
+        return self.client.transport if self.client else lambda: ''
 
     def emit(self, event, data=None):
         """Emit an event to the server.