code: def run_powerflow(self, session, method='onthefly', export_pypsa=False, debug=False):
          
  
          if method == 'db':
              # Empty tables
              pypsa_io.delete_powerflow_tables(session)
  
              for grid_district in self.mv_grid_districts():
                  if export_pypsa:
                      export_pypsa_dir = repr(grid_district.mv_grid)
                  else:
                      export_pypsa_dir = None
                  grid_district.mv_grid.run_powerflow(session, method='db',
                                                      export_pypsa_dir=export_pypsa_dir,
                                                      debug=debug)
  
          elif method == 'onthefly':
              for grid_district in self.mv_grid_districts():
                  if export_pypsa:
                      export_pypsa_dir = repr(grid_district.mv_grid)
                  else:
                      export_pypsa_dir = None
                  grid_district.mv_grid.run_powerflow(session,
                                                      method='onthefly',
                                                      export_pypsa_dir=export_pypsa_dir,
                                                      debug=debug)
docs: Performs power flow calculation for all MV grids
  
          Args:
              session : sqlalchemy.orm.session.Session
                  Database session
              method: str
                  Specify export method
                  If method='db' grid data will be exported to database
                  
                  If method='onthefly' grid data will be passed to PyPSA directly (default)
          export_pypsa: bool
              If True PyPSA networks will be exported as csv to output/debug/grid/<MV-GRID_NAME>/
          debug: bool, defaults to False
              If True, information is printed during process