'Returns the weight of each partition as calculated from the
total weight of all the devices.'

def weight_of_one_part(self):

    try:
        return ((self.parts * self.replicas) / sum((d['weight'] for d in self._iter_devs())))
    except ZeroDivisionError:
        raise exceptions.EmptyRingError('There    are    no    devices    in    this    ring,    or    all    devices    have    been    deleted')
