Only apply the singleuser hub modifications if needed (#42)

jupyterlab_gallery/app.py

@@ -12,8 +12,9 @@ def make_singleuser_app(cls):
         return cls
 
 
-# if jupyterhub is installed, apply jupyterhub patches
-ServerAppClass = make_singleuser_app(ServerApp)
+class classproperty(property):
+    def __get__(self, owner_self, owner_cls):
+        return self.fget(owner_cls)
 
 
 class GalleryApp(ExtensionApp):
@@ -41,7 +42,18 @@ def initialize_handlers(self):
 
         self.log.info(f"Registered {self.name} server extension")
 
-    serverapp_class = ServerAppClass
+    @classproperty
+    def serverapp_class(cls):
+        """If jupyterhub is installed, apply the jupyterhub patches,
+
+        but only do this when this property is accessed, which is when
+        the gallery is used as a standalone app.
+        """
+        if cls._server_cls is None:
+            cls._server_cls = make_singleuser_app(ServerApp)
+        return cls._server_cls
+
+    _server_cls = None
 
     @classmethod
     def make_serverapp(cls, **kwargs) -> ServerApp:
@@ -52,7 +64,7 @@ def make_serverapp(cls, **kwargs) -> ServerApp:
         code (`kernels` service).
         """
         server_app = super().make_serverapp(**kwargs)
-        assert isinstance(server_app, ServerAppClass)
+        assert isinstance(server_app, cls.serverapp_class)
         assert len(server_app.default_services) > 1
         server_app.default_services = ("auth", "security")
         return server_app