code: def _check_operators(self):
          
  
          if not isinstance(self._operators, (list, tuple, np.ndarray)):
              raise TypeError(('Input operators must be provided as a list, '
                               'not {}').format(type(self._operators)))
  
          for op in self._operators:
              if not hasattr(op, 'cost'):
                  raise ValueError('Operators must contain "cost" method.')
              op.cost = check_callable(op.cost)
docs: Check Operators
  
          This method checks if the input operators have a "cost" method
  
          Raises
          ------
          ValueError
              For invalid operators type
          ValueError
              For operators without "cost" method