There is a problem in choosing sound_card.

[iwrose]

 try:
        if subprocess.check_output('amixer | grep PCM'):
            sound_card = "PCM"
    except:
        sound_card = "Master"

the line "if subprocess.check_output('amixer | grep PCM'):¨ should be modified to:
if subprocess.check_output('amixer | grep PCM',shell='true'):

otherwise: it will choose Master but not PCM in my raspberry pi.

[taizilongxu]

Thanks very much! I will update in next version.