title: how to delete an actor in vtk?
body: <p>For example,
  if i have a cube</p>
  
  <p>(this part of code is from the vtk python example)</p>
  
  <pre><code>import vtk
  
  # create a rendering window and renderer
  ren = vtk.vtkRenderer()
  renWin = vtk.vtkRenderWindow()
  renWin.AddRenderer(ren)
  
  # create a renderwindowinteractor
  iren = vtk.vtkRenderWindowInteractor()
  iren.SetRenderWindow(renWin)
  
  # create cube
  cube = vtk.vtkCubeSource()
  
  # mapper
  cubeMapper = vtk.vtkPolyDataMapper()
  cubeMapper.SetInput(cube.GetOutput())
  
  # actor
  cubeActor = vtk.vtkActor()
  cubeActor.SetMapper(cubeMapper)
  
  # assign actor to the renderer
  ren.AddActor(cubeActor)
  
  # enable user interface interactor
  iren.Initialize()
  renWin.Render()
  iren.Start()
  </code></pre>
  
  <p>How can i delete this cube actor and add another one?
  (This has to be done in order)</p>