code: def _load_file(self, filename):
          
          filename = os.path.abspath(os.path.expanduser(filename))
          # test if file exists
          if not os.path.isfile(filename):
              raise Exception('File %s does not exist' % filename)
  
          # Get extension
          ext = vtki.get_ext(filename)
          # Extensions: .vtm and .vtmb
  
          # Select reader
          if ext in ['.vtm', '.vtmb']:
              reader = vtk.vtkXMLMultiBlockDataReader()
          else:
              raise IOError('File extension must be either "vtm" or "vtmb"')
  
          # Load file
          reader.SetFileName(filename)
          reader.Update()
          self.ShallowCopy(reader.GetOutput())
docs: Load a vtkMultiBlockDataSet from a file (extension ``.vtm`` or
          ``.vtmb``)