code: def merge( self, other_cluster ):
          
          new_cluster = Cluster( self.sites | other_cluster.sites )
          new_cluster.neighbours = ( self.neighbours | other_cluster.neighbours ).difference( new_cluster.sites )
          return new_cluster
docs: Combine two clusters into a single cluster.
  
          Args:
              other_cluster (Cluster): The second cluster to combine.
  
          Returns:
              (Cluster):   The combination of both clusters.