Use a non-capturing group by default (#1060)

Now clients don't have to decide whether they need parentheses or not.

beets/util/__init__.py

@@ -681,8 +681,11 @@ def max_filename_length(path, limit=MAX_FILENAME_LENGTH):
 
 
 def feat_tokens(for_artist=True):
-    """Returns the tokens to use to detect featuring artists in strings."""
-
+    """Return a regular expression that matches phrases like "featuring"
+    that separate a main artist or a song title from secondary artists.
+    The `for_artist` option determines whether the regex should be
+    suitable for matching artist fields (the default) or title fields.
+    """
     feat_special_chars = ['&', 'feat.', 'ft.']
     feat_words = ['ft', 'featuring', 'feat']
     if for_artist:  # appending to artist name enables more tokens
@@ -691,4 +694,4 @@ def feat_tokens(for_artist=True):
     if for_artist:
         regex = r'%s|%s' % \
             ('|'.join([re.escape(x) for x in feat_special_chars]), regex)
-    return regex
+    return '(?:{0})'.format(regex)

beetsplug/lyrics.py

@@ -138,7 +138,7 @@ def search_pairs(item):
     artists = [artist]
 
     # Remove any featuring artists from the artists name
-    pattern = r"(.*?) (%s)" % feat_tokens()
+    pattern = r"(.*?) {0}".format(feat_tokens())
     match = re.search(pattern, artist, re.IGNORECASE)
     if match:
         artists.append(match.group(1))
@@ -151,7 +151,7 @@ def search_pairs(item):
         titles.append(match.group(1))
 
     # Remove any featuring artists from the title
-    pattern = r"(.*?) (%s)" % feat_tokens(for_artist=False)
+    pattern = r"(.*?) {0}".format(feat_tokens(for_artist=False))
     for title in titles[:]:
         match = re.search(pattern, title, re.IGNORECASE)
         if match: