vtkMultiPieceDataSet does not work with HyperTree Grid
If a hypertree grid is set as a piece in a VTKMultiPieceDataSet, retrieving it will always return 0. If an unstructured grid is used instead, you can retrieve the piece. @patchett2002 @cory.quammen
For example, in the following code snippet, the variable htgrid2 will always be None
import vtk
htgrid = vtk.vtkHyperTreeGrid()
htgrid.Initialize()
multipiece = vtk.vtkMultiPieceDataSet()
multipiece.SetNumberOfPieces(1)
multipiece.SetPiece(0, htgrid)
htgrid2 = multipiece.GetPiece(0)
print('----- first object -----')
print(htgrid)
print('----- second object -----')
print(htgrid2)