code: def active_scalar_info(self):
          
          if not hasattr(self, '_active_scalar_info'):
              self._active_scalar_info = [POINT_DATA_FIELD, None] # field and name
          field, name = self._active_scalar_info
  
          # rare error where scalar name isn't a valid scalar
          if name not in self.point_arrays:
              if name not in self.cell_arrays:
                  name = None
  
          if name is None:
              if self.n_scalars < 1:
                  return field, name
              # find some array in the set field
              parr = self.GetPointData().GetArrayName(0)
              carr = self.GetCellData().GetArrayName(0)
              if parr is not None:
                  self._active_scalar_info = [POINT_DATA_FIELD, parr]
                  self.GetPointData().SetActiveScalars(parr)
              elif carr is not None:
                  self._active_scalar_info = [CELL_DATA_FIELD, carr]
                  self.GetCellData().SetActiveScalars(carr)
          return self._active_scalar_info
docs: Return the active scalar's field and name: [field, name]