Return the active scalar's field and name: [field, name]

def active_scalar_info(self):
        """Return the active scalar's field and name: [field, name]"""
        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