code: def save(self, filename, binary=True):
          
          filename = os.path.abspath(os.path.expanduser(filename))
          # Use legacy writer if vtk is in filename
          if '.vtk' in filename:
              writer = vtk.vtkRectilinearGridWriter()
              legacy = True
          elif '.vtr' in filename:
              writer = vtk.vtkXMLRectilinearGridWriter()
              legacy = False
          else:
              raise Exception('Extension should be either ".vtr" (xml) or' +
                              '".vtk" (legacy)')
          # Write
          writer.SetFileName(filename)
          writer.SetInputData(self)
          if binary and legacy:
              writer.SetFileTypeToBinary()
          writer.Write()
docs: Writes a rectilinear grid to disk.
  
          Parameters
          ----------
          filename : str
              Filename of grid to be written.  The file extension will select the
              type of writer to use.  ".vtk" will use the legacy writer, while
              ".vtr" will select the VTK XML writer.
  
          binary : bool, optional
              Writes as a binary file by default.  Set to False to write ASCII.
  
  
          Notes
          -----
          Binary files write much faster than ASCII, but binary files written on
          one system may not be readable on other systems.  Binary can be used
          only with the legacy writer.