returns rates

def status(self):
        '''returns rates'''
        counts = {}
        for bucket in self.buckets:
            for x in bucket:
                if not x in counts:
                    counts[x] = 0
                counts[x] += bucket[x]

        ret = ""
        mtypes = counts.keys()
        mtypes.sort()
        for mtype in mtypes:
            ret += "%s: %0.1f/s\n" % (mtype,
                                      counts[mtype]/float(len(self.buckets)))
        return ret