def diff_clusters(self, prev):
    removed = [k for k in prev.clusters if (k not in self.clusters)]
    added = [k for k in self.clusters if (k not in prev.clusters)]
    updated = [k for k in prev.clusters if ((k in self.clusters) and prev.clusters[k].is_different(self.clusters[k]))]
    return (removed, added, updated)
def diff_clusters(self, prev):
    removed = [k for k in prev.clusters if (k not in self.clusters)]
    added = [k for k in self.clusters if (k not in prev.clusters)]
    updated = [k for k in prev.clusters if ((k in self.clusters) and prev.clusters[k].is_different(self.clusters[k]))]
    return (removed, added, updated)