Use segmentations in CAD or FEM software

Support
34

I cannot really follow what you are trying to do, but you can find complete example of extracting submesh corresponding to a specific material here:

# Extract submeshes corresponding to 2 different material Ids
cellData.SetActiveScalars( "Material Id" )
threshold2 = vtkThreshold()
threshold2.SetInputData( mesh )
threshold2.SetInputArrayToProcess(0, 0, 0, vtkDataObject.FIELD_ASSOCIATION_CELLS, vtkDataSetAttributes.SCALARS );
threshold2.ThresholdByLower( 2 )
threshold2.Update()
meshMat2 = threshold2.GetOutput()
threshold3 = vtkThreshold()
threshold3.SetInputData( mesh )
threshold3.SetInputArrayToProcess(0, 0, 0, vtkDataObject.FIELD_ASSOCIATION_CELLS, vtkDataSetAttributes.SCALARS );
threshold3.ThresholdByUpper( 3 )
threshold3.Update()
meshMat3 = threshold3.GetOutput()