lastgenre: _filter_valid forbids genres via helper

- Helper _is_forbidden (similar to _is_valid) checks whether a genre and
  artist combination is forbidden.
- A special artist name "*" can be included in blacklist.yaml to support
  kicking out via the blacklist (and not only the whitelist). TODO: Is
  that redundant or convenient?

Author: JOJ0

beetsplug/lastgenre/__init__.py

@@ -156,7 +156,7 @@ def setup(self):
         if bl_filename:
             bl_filename = normpath(bl_filename)
             try:
-                with codecs.open(bl_filename, 'r', encoding='utf-8') as f:
+                with codecs.open(bl_filename, "r", encoding="utf-8") as f:
                     self.blacklist = yaml.safe_load(f)
                 self._log.debug("Loaded genre blacklist from {0}", bl_filename)
             except Exception as exc:
@@ -265,10 +265,19 @@ def fetch_genre(self, lastfm_obj):
         min_weight = self.config["min_weight"].get(int)
         return self._tags_for(lastfm_obj, min_weight)
 
-    def _filter_valid_genres(self, genres: list[str]) -> list[str]:
-        """Filter list of genres, only keep valid."""
+    def _filter_valid_genres(
+        self, genres: list[str], artist: str = None
+    ) -> list[str]:
+        """Filter list of genres, only keep valid.
+        First applies blacklist filtering if enabled, then whitelist filtering."""
         if not genres:
             return []
+
+        # First remove forbidden genres if we have an artist
+        if artist:
+            genres = [g for g in genres if not self._is_forbidden(g, artist)]
+
+        # Then apply whitelist filter
         return [x for x in genres if self._is_valid(x)]
 
     def _is_valid(self, genre: str) -> bool:
@@ -281,6 +290,33 @@ def _is_valid(self, genre: str) -> bool:
             return True
         return False
 
+    def _is_forbidden(self, genre: str, artist: str) -> bool:
+        """Return True if the genre is forbidden for the artist.
+
+        Supports a special '*' key in the blacklist YAML file for
+        global forbidden genres.
+
+        Example:
+            "Artist Name":
+              - "pop"
+            "*":
+              - "spoken word"
+        """
+        if not self.blacklist:
+            return False
+
+        forbidden = set()
+        # Add global forbidden genres
+        if "*" in self.blacklist:
+            forbidden.update(g.lower() for g in self.blacklist["*"] or [])
+        # Add artist-specific forbidden genres
+        if artist:
+            for bl_artist, blocked_genres in self.blacklist.items():
+                if bl_artist != "*" and bl_artist.lower() == artist.lower():
+                    forbidden.update(g.lower() for g in blocked_genres or [])
+
+        return genre.lower() in forbidden
+
     # Cached last.fm entity lookups.
 
     def _last_lookup(self, entity, method, *args):
@@ -311,25 +347,29 @@ def fetch_album_genre(self, obj):
         return self._filter_valid_genres(
             self._last_lookup(
                 "album", LASTFM.get_album, obj.albumartist, obj.album
-            )
+            ),
+            obj.albumartist,
         )
 
     def fetch_album_artist_genre(self, obj):
         """Return the album artist genre for this Item or Album."""
         return self._filter_valid_genres(
-            self._last_lookup("artist", LASTFM.get_artist, obj.albumartist)
+            self._last_lookup("artist", LASTFM.get_artist, obj.albumartist),
+            obj.albumartist,
         )
 
     def fetch_artist_genre(self, item):
         """Returns the track artist genre for this Item."""
         return self._filter_valid_genres(
-            self._last_lookup("artist", LASTFM.get_artist, item.artist)
+            self._last_lookup("artist", LASTFM.get_artist, item.artist),
+            item.artist,
         )
 
     def fetch_track_genre(self, obj):
         """Returns the track genre for this Item."""
         return self._filter_valid_genres(
-            self._last_lookup("track", LASTFM.get_track, obj.artist, obj.title)
+            self._last_lookup("track", LASTFM.get_track, obj.artist, obj.title),
+            obj.artist,
         )
 
     # Main processing: _get_genre() and helpers.