def scaleSTL(filenameSTL, opacity=0.75, scale=(1,1,1), mesh_color="gold"):
    colors = vtk.vtkNamedColors()

    reader = vtk.vtkSTLReader()
    reader.SetFileName(filenameSTL)
    reader.Update()

    transform = vtk.vtkTransform()
    transform.Scale(scale)

    transformFilter = vtk.vtkTransformPolyDataFilter()
    transformFilter.SetInputConnection(reader.GetOutputPort())
    transformFilter.SetTransform(transform)
    transformFilter.Update()

    mapper = vtk.vtkPolyDataMapper()
    mapper.SetInputConnection(transformFilter.GetOutputPort())

    actor = vtk.vtkActor()
    actor.SetMapper(mapper)
    actor.GetProperty().SetColor(colors.GetColor3d(mesh_color))
    actor.GetProperty().SetOpacity(opacity)

    return actor

def render_scene(my_actor_list):
    renderer = vtk.vtkRenderer()
    for arg in my_actor_list:
        renderer.AddActor(arg)
    namedColors = vtk.vtkNamedColors()
    renderer.SetBackground(namedColors.GetColor3d("SlateGray"))

    window = vtk.vtkRenderWindow()
    window.SetWindowName("Oriented Cylinder")
    window.AddRenderer(renderer)

    interactor = vtk.vtkRenderWindowInteractor()
    interactor.SetRenderWindow(window)

    # Visualize
    window.Render()
    interactor.Start()

if __name__ == "__Main__":

    filename = "400_tri.stl"
    scale01 = (1, 1, 1)
    scale02 = (0.5, 0.5, 0.5)
    my_list = []
    my_list.append(scaleSTL(filename, 0.75, scale01, "Gold"))
    my_list.append(scaleSTL(filename, 0.75, scale02, "DarkGreen"))
    render_scene(my_list)