Reading data from a raw VTK (.vtu) file

I want to extract data arrays from a .vtu file using the Python VTK module. The file looks like this (the raw data at the end of the file is ommitted):

<?xml version="1.0"?> <VTKFile type="UnstructuredGrid" version="0.1" byte_order="LittleEndian">   <UnstructuredGrid>     <Piece NumberOfPoints="10471" NumberOfCells="64892">       <PointData>         <DataArray type="Float64" Name="potential" NumberOfComponents="1" format="appended" offset="0"/>         <DataArray type="Float64" Name="electric field" NumberOfComponents="3" format="appended" offset="83772"/>       </PointData>       <CellData>         <DataArray type="Int32" Name="GeometryIds" format="appended" offset="335080"/>       </CellData>       <Points>         <DataArray type="Float64" NumberOfComponents="3" format="appended" offset="594652"/>       </Points>       <Cells>         <DataArray type="Int32" Name="connectivity" format="appended" offset="845960"/>         <DataArray type="Int32" Name="offsets" format="appended" offset="1865068"/>         <DataArray type="Int32" Name="types" format="appended" offset="2124640"/>       </Cells>     </Piece>   </UnstructuredGrid> <AppendedData encoding="raw"> 

I try to extract the data using the following python code:

import numpy from vtk import vtkUnstructuredGridReader from vtk.util import numpy_support as VN  reader = vtkUnstructuredGridReader() reader.SetFileName("charged_wire.vtu") reader.ReadAllVectorsOn() reader.ReadAllScalarsOn() reader.Update()  data = reader.GetOutput() potential = data.GetPointData().GetScalars("potential")  print(type(potential)) 

Unfortunately, this program prints NoneType as output and I’m not really sure what I need to change in order to extract the data stores in the potential array?