code: def update_existing_peers( self, num_to_remove, peer_table=None, con=None, path=None ):
          
          
          if path is None:
              path = self.atlasdb_path
  
          # remove peers that are too old
          if self.last_clean_time + atlas_peer_clean_interval() < time_now():
              # remove stale peers
              log.debug("%s: revalidate old peers" % self.my_hostport)
              atlas_revalidate_peers( con=con, path=path, peer_table=peer_table )
              self.last_clean_time = time_now()
  
          removed = self.remove_unhealthy_peers( num_to_remove, con=con, path=path, peer_table=peer_table )
  
          # if they're also in the new set, remove them there too
          for peer in removed:
              if peer in self.new_peers:
                  self.new_peers.remove(peer)
  
          return len(removed)
docs: Update the set of existing peers:
          * revalidate the existing but old peers
          * remove at most $num_to_remove unhealthy peers
  
          Return the number of peers removed