List all artists in a MP3 directory and subdirectories

mp3artists.py

from os import walk
from mutagen.mp3 import MP3

mypath = '/Volumes/Macintosh HD/Media/Music/iTunes/'
mypath = '/Volumes/Media HD/MP3/'

f = []
artists = []
a = 0
b = 0
output = open('output.txt', 'w')
for (dirpath, dirnames, filenames) in walk(mypath):
    #b += 1
    if filenames:
        for fn in filenames:
            if '.mp3' in fn:
                filepath = '%s/%s' % (dirpath, fn)
                try:
                    audio = MP3(filepath)
                    artist = audio['TPE1'].text[0]
                    if artist not in artists:
                        a += 1
                        print a, artist
                        artists.append(artist)
                        output.write('%s\n' % artist)
                except:
                    pass
    #if b == 20:
    #    break