title: How to write a paraview python programmable source that makes a multiblockDataset?
body: <p>I'm trying to write a python programmable source in Paraview that will create a <code>vtkMultiBlockDataSet</code>. I see that my python script in the programmable source gets a symbol called <code>output</code> which is of type <code>vtk.numpy_interface.dataset_adapter.CompositeDataSet</code>. How do I use that object to set the blocks? The only methods I see are to set things like points and cells. </p>
  
  <p>My code creates a <code>vtk.vtkMultiBlockDataSet</code>. Can I somehow just set <code>output</code> to be this thing that I make?  Or do I need to copy? Thanks for any advice! -- Adam</p>