class_docstr: Class to support multiple render passes for a renderer.
  
  Notes
  -----
  Passes are organized here as "primary" (vtkOpenGLRenderPass) that act
  within the renderer and "post-processing" (vtkImageProcessingPass) passes,
  which act on the image generated from the renderer.
  
  The primary passes are added as part of a vtk.vtkRenderPassCollection or
  are "stacked", while the post-processing passes are added as a final pass
  to the rendered image.
  
  Parameters
  ----------
  renderer : vtk.vtkRenderer
      Renderer to initialize render passes for.
docstr: Initialize (when necessary) the sequence collection and return it.
  
  This lets us lazily generate the sequence collection only when we need it
  rather than at initialization of the class.
docstr_tok: ["Initialize","(","when","necessary",")","the","sequence","collection","and","return","it",".","This","lets","us","lazily","generate","the","sequence","collection","only","when","we","need","it","rather","than","at","initialization","of","the","class","."]
code: def _seq_pass(self):
      """Initialize (when necessary) the sequence collection and return it.
  
      This lets us lazily generate the sequence collection only when we need it
      rather than at initialization of the class.
  
      """
      if self.__seq_pass is None:
          self._init_passes()
      return self.__seq_pass
  
imports: import weakref
  from .None import _vtk
label_desc: Use image node_id 3 for calling the RenderPasses obj's underlying member method code with example usage: obj._seq_pass() and returns: self