            contour = vtkDiscreteFlyingEdges3D()
        except AttributeError:
            contour = vtkDiscreteMarchingCubes()
    else:
        contour = vtkDiscreteMarchingCubes()
    contour.SetInputConnection(voi.GetOutputPort())
--
            discrete_cubes = vtkDiscreteFlyingEdges3D()
        except AttributeError:
            using_marching_cubes = True
            discrete_cubes = vtkDiscreteMarchingCubes()
    else:
        using_marching_cubes = True
--
            discrete = vtkDiscreteFlyingEdges3D()
        except AttributeError:
            discrete = vtkDiscreteMarchingCubes()
    else:
        discrete = vtkDiscreteMarchingCubes()
    discrete.SetInputData(blob)
