'Returns an iterator all the non-None devices in the ring. Note that
this means list(b._iter_devs())[some_id] may not equal b.devs[some_id];
you will have to check the \'id\' key of each device to obtain its
dev_id.'

def _iter_devs(self):

    for dev in self.devs:
        if (dev is not None):
            (yield dev)
