code: def length(self):
          
          cost = 0
          depot = self._problem.depot()
  
          last = depot
          for i in self._nodes:
              a, b = last, i
              if a.name() > b.name():
                  a, b = b, a
  
              cost = cost + self._problem.distance(a, b)
              last = i
  
          cost = cost + self._problem.distance(depot, last)
  
          return cost
docs: Returns the route length (cost)
          
          Returns
          -------
          int
              Route length (cost).