code: def save(self, filename, binary=True):
          
          filename = os.path.abspath(os.path.expanduser(filename))
          ext = vtki.get_ext(filename)
          if ext in ['.vtm', '.vtmb']:
              writer = vtk.vtkXMLMultiBlockDataWriter()
          else:
              raise Exception('File extension must be either "vtm" or "vtmb"')
  
          writer.SetFileName(filename)
          writer.SetInputDataObject(self)
          if binary:
              writer.SetDataModeToBinary()
          else:
              writer.SetDataModeToAscii()
          writer.Write()
          return
docs: Writes a ``MultiBlock`` dataset to disk.
  
          Written file may be an ASCII or binary vtm file.
  
          Parameters
          ----------
          filename : str
              Filename of mesh to be written.  File type is inferred from
              the extension of the filename unless overridden with
              ftype.  Can be one of the following types (.vtm or .vtmb)
  
          binary : bool, optional
              Writes the file as binary when True and ASCII when False.
  
          Notes
          -----
          Binary files write much faster than ASCII and have a smaller
          file size.