def filter_song_md(song, md_list=[u'id'], no_singletons=True):
 filtered = [song[md_type] for md_type in md_list]
 if ((len(md_list) == 1) and no_singletons):
  return filtered[0]
 else:
  return filtered

def filter_song_md ( song , md_list = [ u'id' ] , no_singletons = True ) : filtered = [ song [ md_type ] for md_type in md_list ] if ( ( len ( md_list ) == 1 ) and no_singletons ) : return filtered [ 0 ] else : return filtered
returns a list of desired metadata from a song .