<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def _cell_scalar(self, name=None):
 """ Returns the cell scalars of a vtk object Parameters name : str Name of cell scalars to retrive. Returns ------- scalars : np.ndarray Numpy array of scalars """

        if name is None:
            # use active scalar array
            field, name = self.active_scalar_info
            if field != CELL_DATA_FIELD:
                raise RuntimeError('Must specify an array to fetch.')

        vtkarr = self.GetCellData().GetArray(name)
        if vtkarr is None:
            raise AssertionError('({}) is not a cell scalar'.format(name))

        # numpy does not support bit array data types
        if isinstance(vtkarr, vtk.vtkBitArray):
            vtkarr = vtk_bit_array_to_char(vtkarr)
            if name not in self._cell_bool_array_names:
                self._cell_bool_array_names.append(name)

        array = vtk_to_numpy(vtkarr)
        if array.dtype == np.uint8 and name in self._cell_bool_array_names:
            array = array.view(np.bool)
        return array