code: def export_for_schema(self):
          
          ret = "{'class': 'NetworkTopologyStrategy'"
          for dc, repl_factor in sorted(self.dc_replication_factors.items()):
              ret += ", '%s': '%d'" % (dc, repl_factor)
          return ret + "}"
docs: Returns a string version of these replication options which are
          suitable for use in a CREATE KEYSPACE statement.