code: def atlas_rank_peers_by_data_availability( peer_list=None, peer_table=None, local_inv=None, con=None, path=None ):
      
  
      with AtlasPeerTableLocked(peer_table) as ptbl:
          if peer_list is None:
              peer_list = ptbl.keys()[:]
  
          if local_inv is None:
              # what's my inventory?
              inv_len = atlasdb_zonefile_inv_length( con=con, path=path )
              local_inv = atlas_make_zonefile_inventory( 0, inv_len, con=con, path=path )
  
          peer_availability_ranking = []    # (health score, peer hostport)
          for peer_hostport in peer_list:
  
              peer_inv = atlas_peer_get_zonefile_inventory( peer_hostport, peer_table=ptbl )
  
              # ignore peers that we don't have an inventory for
              if len(peer_inv) == 0:
                  continue
  
              availability_score = atlas_inventory_count_missing( local_inv, peer_inv )
              peer_availability_ranking.append( (availability_score, peer_hostport) )
      
  
      # sort on availability
      peer_availability_ranking.sort()
      peer_availability_ranking.reverse()
  
      return [peer_hp for _, peer_hp in peer_availability_ranking]
docs: Get a ranking of peers to contact for a zonefile.
      Peers are ranked by the number of zonefiles they have
      which we don't have.
  
      This is used to select neighbors.