code: def _cost_method(self, *args, **kwargs):
          
  
          return np.sum([operator.cost(data) for operator, data in
                         zip(self.operators, args[0])])
docs: Calculate combined proximity operator components of the cost
  
          This method returns the sum of the cost components from each of the
          proximity operators
  
          Returns
          -------
          float combinded cost components