docs: def init_mv_grid(mv_grid_districts=[3545], filename='ding0_tests_grids_1.pkl'):
      '''Runs ding0 over the districtis selected in mv_grid_districts
  
      It also writes the result in filename. If filename = False,
      then the network is not saved.
  
      Parameters
      ----------
      mv_grid_districts: :any:`list` of :obj:`int`
          Districts IDs: Defaults to [3545]
      filename: str
          Defaults to 'ding0_tests_grids_1.pkl'
          If filename=False, then the network is not saved
  
      Returns
      -------
      NetworkDing0
          The created MV network.
  
      '''
      print('\n########################################')
      print('  Running ding0 for district', mv_grid_districts)
      # database connection/ session
      engine = db.connection(section='oedb')
      session = sessionmaker(bind=engine)()
  
      # instantiate new ding0 network object
      nd = NetworkDing0(name='network')
  
      # run DINGO on selected MV Grid District
      nd.run_ding0(session=session, mv_grid_districts_no=mv_grid_districts)
  
      # export grid to file (pickle)
      if filename:
          print('\n########################################')
          print('  Saving result in ', filename)
          save_nd_to_pickle(nd, filename=filename)
  
      print('\n########################################')
      return nd