diff --git a/jupyterhub/singleuser/__init__.py b/jupyterhub/singleuser/__init__.py
index dcd8c332..f3188bc7 100644
--- a/jupyterhub/singleuser/__init__.py
+++ b/jupyterhub/singleuser/__init__.py
@@ -5,7 +5,12 @@ Contains default notebook-app subclass and mixins
 from .app import SingleUserNotebookApp, main
 from .mixins import HubAuthenticatedHandler, make_singleuser_app
 
-__all__ = ["SingleUserNotebookApp", "main", "HubAuthenticatedHandler", "make_singleuser_app"]
+__all__ = [
+    "SingleUserNotebookApp",
+    "main",
+    "HubAuthenticatedHandler",
+    "make_singleuser_app",
+]
 
 # backward-compatibility
 JupyterHubLoginHandler = SingleUserNotebookApp.login_handler_class