docs: def busmap_from_psql(network, session, scn_name):
      """ Retrieves busmap from `model_draft.ego_grid_pf_hv_busmap` on the
      <OpenEnergyPlatform>[www.openenergy-platform.org] by a given scenario
      name. If this busmap does not exist, it is created with default values.
  
      Parameters
      ----------
      network : pypsa.Network object
          Container for all network components.
  
      session : sqlalchemy.orm.session.Session object
          Establishes interactions with the database.
  
      scn_name : str
          Name of the scenario.
  
      Returns
      -------
      busmap : dict
          Maps old bus_ids to new bus_ids.
      """
  
      def fetch():
  
          query = session.query(EgoGridPfHvBusmap.bus0, EgoGridPfHvBusmap.bus1).\
              filter(EgoGridPfHvBusmap.scn_name == scn_name)
  
          return dict(query.all())
  
      busmap = fetch()
  
      # TODO: Or better try/except/finally
      if not busmap:
          print('Busmap does not exist and will be created.\n')
  
          cpu_cores = input('cpu_cores (default 4): ') or '4'
  
          busmap_by_shortest_path(network, session, scn_name,
                                  fromlvl=[110], tolvl=[220, 380, 400, 450],
                                  cpu_cores=int(cpu_cores))
          busmap = fetch()
  
      return busmap