code: def load_inv_result(self, filename, columns=2):
          
          assert os.path.isfile(filename)
          try:
              iterator = iter(columns)
          except TypeError:
              # not iterable
              iterator = [columns, ]
  
          pid_list = []
          for column in iterator:
              data = np.loadtxt(filename, skiprows=1)
              pid = self.add_data(data[:, column])
              pid_list.append(pid)
  
          if len(pid_list) == 1:
              return pid_list[0]
          else:
              return pid_list
docs: Load one parameter set from a rho*.mag or rho*.pha file produced by
          CRTomo.
  
          Parameters
          ----------
          filename : string, file path
              Filename to loaded data from
          columns : int or iterable of ints, optional
              column(s) to add to the manager. Defaults to 2 (third column).
  
          Returns
          -------
          pid : int or list of ints
              ID(s) of parameter set