add assertion for more consistency

xtreemfs_client/dataDistribution.py

@@ -62,6 +62,10 @@ class DataDistribution(object):
         :param osd_capacities: map from osd uuids to osd capacities
         :return:
         """
+        # make sure that the keyset of self.OSDs matches the keyset of osd_capacities
+        for osd_uuid in osd_capacities:
+            assert osd_uuid in self.OSDs.keys()
+        assert len(self.OSDs) == len(osd_capacities)
         for one_osd in self.OSDs.values():
             assert type(osd_capacities[one_osd.uuid]) is int
             one_osd.capacity = osd_capacities[one_osd.uuid]