Support generators in MetadataSourcePlugin.get_artist method

beets/plugins.py

@@ -685,6 +685,8 @@ def get_artist(artists, id_key='id', name_key='name', join_key=None):
         """
         artist_id = None
         artist_string = ""
+        # Count items (supports generators as well as lists, dicts, ...)
+        total = sum(1 for _ in artists)
         for idx, artist in enumerate(artists):
             if not artist_id:
                 artist_id = artist[id_key]
@@ -694,7 +696,7 @@ def get_artist(artists, id_key='id', name_key='name', join_key=None):
             # Move articles to the front.
             name = re.sub(r'^(.*?), (a|an|the)$', r'\2 \1', name, flags=re.I)
             # Use a join keyword if requested and available.
-            if idx < (len(artists) - 1):  # Skip joining on last.
+            if idx < (total - 1):  # Skip joining on last.
                 if join_key and artist.get(join_key, None):
                     name += " " + artist[join_key] + " "
                 else: