AttributeError: AS Instance has no attribute 'toString'

Question

Writing code in Python for an Astar program to find the shortest path between cities. Getting the above error, and I'm at a complete loss. Pulling between a few .py files, here are the relevant sections:

from asdriver.py - added full asdriver

import adata   # Map data
import astar   # A* class
import sys

# Default start, goal cities
defaultcities = ('Yakima, WA', 'Tampa, FL')

def printnode(n):
    print n.toString()

adata.input()

startcity = raw_input("Start city [{0}]: ".format(defaultcities[0])).strip()
if startcity == '':  startcity = defaultcities[0]
if startcity not in adata.cities:
     print "City not recognized"
     sys.exit(0)

goalcity = raw_input("Goal city [{0}]: ".format(defaultcities[1])).strip()
if goalcity == '':  goalcity = defaultcities[1] 
if goalcity not in adata.cities:
    print "City not recognized"
    sys.exit(0)

dbg = raw_input("Debug Options: [none]").strip()

findpath = astar.AS(startcity, goalcity, printnode)
ans = findpath.astar_run(printnode, dbg)
    if not ans:
        print "No answer"
    else:
        print "Final Path:"
        print ans.toString()

From astar.py

 import adata

 class AS:
     def __init__(self, startcity, goalcity, tracefunc):
        self.startcity = startcity
        self.goalcity = goalcity
        self.tracefunc = tracefunc
        self.openlist = [Node([startcity])]
        self.closedlist = []

     def heuristic(self, printnode, start, end):
        raise NotImplementedError

     def astar_run(self, startcity, endcity, dbg = ""):
        while self.openlist:
            citystep = min(self.openlist, key = lambda o:o.g + o.h)
            if citystep == self.goalcity:
                 path = []
                 while citystep.parent:
                path.append(citystep)
                citystep = citystep.parent
            path.append(citystep)
            return path[::-1]
        self.openlist.remove(citystep)
        self.closedlist.append(citystep)
        for printnode in self.openlist:   #was self.tracefunc
            if printnode in self.closedset:
                continue
            elif printnode in self.openset:
                newG = citystep.g + citystep.cost(printnode)
                if printnode.g > newG:
                    printnode.g = newG
                    printnode.parent = citystep
                else:
                    printnode.g = citystep.g + citystep.cost(printnode)
                    printnode.h = self.heuristic(printnode, start, end)
                    printnode.parent = citystep
                    self.openset.add(printnode)
        return self    



class Node:
def __init__(self, path=[], f=0, g=0, h=0):
    self.path = path[:]
    self.f = f
    self.g = g
    self.h = h
    self.parent = None

def toString(self):
    s = 'f=%d g=%d h=%d ' % (self.f, self.g, self.h)
    for city in self.path:
        s = s + ' ' + city
    return s

def cost(self):
    raise NotImplementedError

'

Complete beginner, so any help would be appreciated.

Thanks in advance!!!

Answer 1

Your def astar_run() method returns self (see last line of your method), or it returns a list by slicing the path[::-1], neither has a toString() method so you are getting this exception. If you want to print the representation of your class then it is normal to declare this method __repr__() and then you can just print ans. If you want to be able to convert to a string then the method is usually called __str__().

What do you expect to be return from astar_run()? It is usually poor practice to return two different types from the same function.