Typing lessons like duolingo & musicmouse cleanup

python-backend/musicmouse/__main__.py

@@ -297,13 +297,17 @@ def _build_app(
     return app
 
 
+def _service_of_type[T: Service](services: list[Service], kind: type[T]) -> T | None:
+    return next((s for s in services if isinstance(s, kind)), None)
+
+
 def _analysis_batch_hook(services: list[Service]) -> Callable[[], Awaitable[None]] | None:
     """The web front-end's own hub, if it is running - so open tabs refetch the library
     as background analysis lands, instead of only after a manual reload. `None` when
     there is no web service, which `MusicLibrary.analyze_pending` treats as "nobody to
     tell".
     """
-    web_service = next((s for s in services if isinstance(s, WebService)), None)
+    web_service = _service_of_type(services, WebService)
     return web_service.hub.broadcast_library if web_service else None
 
 
@@ -339,7 +343,7 @@ def _build_services(
 
     # Unconditional: a show only starts downloading once someone drops a `feed.txt`
     # into its folder, so there is nothing to gate here with its own config section.
-    web_service = next((s for s in services if isinstance(s, WebService)), None)
+    web_service = _service_of_type(services, WebService)
     services.append(
         PodcastFeedService(
             app.library,