make page_config_hook optional

voila/app.py

@@ -349,18 +349,25 @@ def hook(req: tornado.web.RequestHandler,
         ),
     )
 
-    get_page_config_hook = Callable(
-        default_value=lambda page_config, **kwargs: page_config,
+    page_config_hook = Callable(
+        default_value=None,
+        allow_none=True,
         config=True,
         help=_(
             """A function that is called to modify the page config for a given notebook.
             Should be of the form:
 
-            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.
+            def page_config_hook(
+                base_url: str,
+                settings: Dict[str, Any],
+                log: Logger,
+                voila_configuration: VoilaConfiguration,
+                notebook_path: str
+            ) -> Dict[str, Any]:
+
+            The hook receives the default page_config dictionary and all its parameters, it 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.
             """
         ),
     )
@@ -631,7 +638,7 @@ def init_settings(self) -> Dict:
             self.voila_configuration.multi_kernel_manager_class,
             preheat_kernel,
             pool_size,
-            get_page_config_hook=self.get_page_config_hook,
+            page_config_hook=self.page_config_hook,
         )
         self.kernel_manager = kernel_manager_class(
             parent=self,
@@ -807,7 +814,7 @@ def init_handlers(self) -> List:
                         "config": self.config,
                         "voila_configuration": self.voila_configuration,
                         "prelaunch_hook": self.prelaunch_hook,
-                        "get_page_config_hook": self.get_page_config_hook,
+                        "page_config_hook": self.page_config_hook,
                     },
                 )
             )
@@ -820,15 +827,15 @@ def init_handlers(self) -> List:
                         TornadoVoilaTreeHandler,
                         {
                             "voila_configuration": self.voila_configuration,
-                            "get_page_config_hook": self.get_page_config_hook,
+                            "page_config_hook": self.page_config_hook,
                         },
                     ),
                     (
                         url_path_join(self.server_url, r"/voila/tree" + path_regex),
                         TornadoVoilaTreeHandler,
                         {
                             "voila_configuration": self.voila_configuration,
-                            "get_page_config_hook": self.get_page_config_hook,
+                            "page_config_hook": self.page_config_hook,
                         },
                     ),
                     (
@@ -839,7 +846,7 @@ def init_handlers(self) -> List:
                             "config": self.config,
                             "voila_configuration": self.voila_configuration,
                             "prelaunch_hook": self.prelaunch_hook,
-                            "get_page_config_hook": self.get_page_config_hook,
+                            "page_config_hook": self.page_config_hook,
                         },
                     ),
                     # On serving a directory, expose the content handler.

voila/handler.py

@@ -73,9 +73,7 @@ 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_hook = kwargs.get(
-            "get_page_config_hook", lambda page_config, **kwargs: page_config
-        )
+        self.page_config_hook = kwargs.get("page_config_hook", None)
 
         # we want to avoid starting multiple kernels due to template mistakes
         self.kernel_started = False
@@ -197,11 +195,15 @@ async def get_generator(self, path=None):
                 "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,
-            )
+
+            page_config = get_page_config(**page_config_kwargs)
+
+            if self.page_config_hook:
+                page_config = self.page_config_hook(
+                    page_config,
+                    **page_config_kwargs,
+                    notebook_path=notebook_path,
+                )
 
             gen = NotebookRenderer(
                 request_handler=self,

voila/tornado/treehandler.py

@@ -23,9 +23,7 @@
 class TornadoVoilaTreeHandler(VoilaTreeHandler):
     def initialize(self, **kwargs):
         super().initialize(**kwargs)
-        self.get_page_config_hook = kwargs.get(
-            "get_page_config_hook", lambda page_config, **kwargs: page_config
-        )
+        self.page_config_hook = kwargs.get("page_config_hook", None)
 
     @web.authenticated
     async def get(self, path=""):
@@ -70,11 +68,16 @@ def allowed_content(content):
                 "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 = get_page_config(**page_config_kwargs)
+
+            if self.page_config_hook:
+                self.page_config_hook(
+                    page_config,
+                    **page_config_kwargs,
+                    notebook_path=path,
+                )
+
             page_config["jupyterLabTheme"] = theme_arg
             page_config["frontend"] = "voila"
             page_config["query"] = self.request.query

voila/utils.py

@@ -95,7 +95,7 @@ def get_page_config(
     settings: Dict[str, Any],
     log: Logger,
     voila_configuration: VoilaConfiguration,
-):
+) -> Dict[str, Any]:
     """Get the page configuration for Voila.
 
     Args:

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 = lambda page_config, **kwargs: page_config,
+    page_config_hook: Callable = None,
 ) -> T:
     """
     Decorator used to make a normal kernel manager compatible with pre-heated
@@ -53,7 +53,7 @@ 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): Hook to modify the default page config.
+        - page_config_hook (Callable, optional): Hook to modify the default page config.
 
     Returns:
         T: Decorated class
@@ -400,11 +400,15 @@ def _notebook_renderer_factory(
                     "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,
-                )
+
+                page_config = get_page_config(**page_config_kwargs)
+
+                if page_config_hook:
+                    page_config = page_config_hook(
+                        page_config,
+                        **page_config_kwargs,
+                        notebook_path=notebook_path,
+                    )
 
                 return NotebookRenderer(
                     voila_configuration=voila_configuration,