use the hook to modify the default get_page function

voila/app.py

@@ -331,24 +331,17 @@ def hook(req: tornado.web.RequestHandler,
     )
 
     get_page_config_hook = Callable(
-        default_value=None,
-        allow_none=True,
+        default_value=lambda page_config, **kwargs: page_config,
         config=True,
         help=_(
-            """A function that is called to get the page config for a given notebook.
+            """A function that is called to modify the page config for a given notebook.
             Should be of the form:
 
-            def hook_fn(
-                base_url: str,
-                settings: Dict[str, Any],
-                log: Logger,
-                voila_configuration: VoilaConfiguration,
-                **kwargs
-            ) -> Dict
-
-            The hook should return a dictionary that will be passed to the template
-            as the `page_config` variable and the NotebookRenderer. This can be used to pass custom
-            configuration.
+            def hook_fn(page_config, **kwargs) -> Dict
+
+            The hook receives the default page_config dictionary and should return a dictionary
+            that will be passed to the template as the `page_config` variable and the
+            NotebookRenderer. This can be used to pass custom configuration.
             """
         ),
     )
@@ -792,7 +785,14 @@ def init_handlers(self) -> List:
             self.log.debug("serving directory: %r", self.root_dir)
             handlers.extend(
                 [
-                    (self.server_url, TornadoVoilaTreeHandler, tree_handler_conf),
+                    (
+                        self.server_url,
+                        TornadoVoilaTreeHandler,
+                        {
+                            "voila_configuration": self.voila_configuration,
+                            "get_page_config_hook": self.get_page_config_hook,
+                        },
+                    ),
                     (
                         url_path_join(self.server_url, r"/voila/tree" + path_regex),
                         TornadoVoilaTreeHandler,

voila/handler.py

@@ -73,7 +73,10 @@ def initialize(self, **kwargs):
         self.traitlet_config = kwargs.pop("config", None)
         self.voila_configuration: VoilaConfiguration = kwargs["voila_configuration"]
         self.prelaunch_hook = kwargs.get("prelaunch_hook", None)
-        self.get_page_config = kwargs.get("get_page_config_hook") or get_page_config
+        self.get_page_config_hook = kwargs.get(
+            "get_page_config_hook", lambda page_config, **kwargs: page_config
+        )
+
         # we want to avoid starting multiple kernels due to template mistakes
         self.kernel_started = False
 
@@ -187,6 +190,19 @@ async def get_generator(self, path=None):
                 return
             mathjax_config = self.settings.get("mathjax_config")
             mathjax_url = self.settings.get("mathjax_url")
+
+            page_config_kwargs = {
+                "base_url": self.base_url,
+                "settings": self.settings,
+                "log": self.log,
+                "voila_configuration": self.voila_configuration,
+            }
+            page_config = self.get_page_config_hook(
+                get_page_config(**page_config_kwargs),
+                **page_config_kwargs,
+                notebook_path=notebook_path,
+            )
+
             gen = NotebookRenderer(
                 request_handler=self,
                 voila_configuration=self.voila_configuration,
@@ -198,13 +214,7 @@ async def get_generator(self, path=None):
                 base_url=self.base_url,
                 kernel_spec_manager=self.kernel_spec_manager,
                 prelaunch_hook=self.prelaunch_hook,
-                page_config=self.get_page_config(
-                    base_url=self.base_url,
-                    settings=self.settings,
-                    log=self.log,
-                    voila_configuration=self.voila_configuration,
-                    notebook_path=notebook_path,
-                ),
+                page_config=page_config,
                 mathjax_config=mathjax_config,
                 mathjax_url=mathjax_url,
             )

voila/tornado/treehandler.py

@@ -23,7 +23,9 @@
 class TornadoVoilaTreeHandler(VoilaTreeHandler):
     def initialize(self, **kwargs):
         super().initialize(**kwargs)
-        self.get_page_config = kwargs.get("get_page_config_hook") or get_page_config
+        self.get_page_config_hook = kwargs.get(
+            "get_page_config_hook", lambda page_config, **kwargs: page_config
+        )
 
     @web.authenticated
     async def get(self, path=""):
@@ -62,11 +64,15 @@ def allowed_content(content):
 
             theme_arg = self.validate_theme(theme_arg, classic_tree)
 
-            page_config = self.get_page_config(
-                base_url=self.base_url,
-                settings=self.settings,
-                log=self.log,
-                voila_configuration=self.voila_configuration,
+            page_config_kwargs = {
+                "base_url": self.base_url,
+                "settings": self.settings,
+                "log": self.log,
+                "voila_configuration": self.voila_configuration,
+            }
+            page_config = self.get_page_config_hook(
+                get_page_config(**page_config_kwargs),
+                **page_config_kwargs,
                 notebook_path=path,
             )
             page_config["jupyterLabTheme"] = theme_arg

voila/utils.py

@@ -95,7 +95,6 @@ def get_page_config(
     settings: Dict[str, Any],
     log: Logger,
     voila_configuration: VoilaConfiguration,
-    **kwargs,
 ):
     """Get the page configuration for Voila.
 
@@ -104,7 +103,6 @@ def get_page_config(
         settings (Dict[str, Any]): The settings of the Voila application.
         log (Logger): The logger instance.
         voila_configuration (VoilaConfiguration): The Voila configuration instance.
-        **kwargs: additional keyword arguments that can be used when get_page_config_hook is set.
     """
     page_config = {
         "appVersion": __version__,

voila/voila_kernel_manager.py

@@ -37,7 +37,7 @@ def voila_kernel_manager_factory(
     base_class: Type[T],
     preheat_kernel: bool,
     default_pool_size: int,
-    get_page_config_hook: Callable = None,
+    get_page_config_hook: Callable = lambda page_config, **kwargs: page_config,
 ) -> T:
     """
     Decorator used to make a normal kernel manager compatible with pre-heated
@@ -53,14 +53,12 @@ def voila_kernel_manager_factory(
         - preheat_kernel (Bool): Flag to decorate the input class
         - default_pool_size (int): Size of pre-heated kernel pool for each notebook.
             Zero or negative number means disabled
-        - get_page_config_hook (Callable, optional): Hook to get the page config.
+        - get_page_config_hook (Callable): Hook to modify the default page config.
 
     Returns:
         T: Decorated class
     """
 
-    get_page_config_fn = get_page_config_hook or get_page_config
-
     if not preheat_kernel:
 
         class NormalKernelManager(base_class):
@@ -395,6 +393,19 @@ def _notebook_renderer_factory(
                 settings = self.parent.app.settings
                 mathjax_config = settings.get("mathjax_config")
                 mathjax_url = settings.get("mathjax_url")
+
+                page_config_kwargs = {
+                    "base_url": self.parent.base_url,
+                    "settings": self.parent.app.settings,
+                    "log": self.parent.log,
+                    "voila_configuration": voila_configuration,
+                }
+                page_config = get_page_config_hook(
+                    get_page_config(**page_config_kwargs),
+                    **page_config_kwargs,
+                    notebook_path=notebook_path,
+                )
+
                 return NotebookRenderer(
                     voila_configuration=voila_configuration,
                     traitlet_config=self.parent.config,
@@ -404,13 +415,7 @@ def _notebook_renderer_factory(
                     contents_manager=self.parent.contents_manager,
                     base_url=self.parent.base_url,
                     kernel_spec_manager=self.parent.kernel_spec_manager,
-                    page_config=get_page_config_fn(
-                        base_url=self.parent.base_url,
-                        settings=self.parent.app.settings,
-                        log=self.parent.log,
-                        voila_configuration=voila_configuration,
-                        notebook_path=notebook_path,
-                    ),
+                    page_config=page_config,
                     mathjax_config=mathjax_config,
                     mathjax_url=mathjax_url,
                 )