Implement unique_id to prevent duplicate devices

homeassistant/components/media_player/sonos.py

@@ -78,6 +78,11 @@ class SonosDevice(MediaPlayerDevice):
         """ Returns the name of the device. """
         return self._name
 
+    @property
+    def unique_id(self):
+        """ Returns a unique id. """
+        return "{}.{}".format(self.__class__, self._player.uid)
+
     @property
     def state(self):
         """ Returns the state of the device. """