Ordering a list by specific subvalues in Python 2.7.5

Question

Edit

I've tried

self.openlist.sort(key = lambda d: (d['f']))

and

import operator
self.openlist.sort(key = operator.itemgetter('f'))

and both crash with AttributeError: Node instance has no attribute 'getitem'

End Edit

It may be due to my general unfamiliarity with Python, but I wasn't able to find an answer to my question via searching, so I am asking here.

I am writing an A* program to find the shortest path between cities.

I am storing all of the cities I can travel to at each step in a list, self.openlist, and as I process them I am assigning them all subvalues, such as self.openlist.g, self.openlist.h, self.openlist.f, and others.

I need to sort self.openlist by the f subvalue, from lowest to highest.

Also, I have a lot of unnecessary print's in there just to help me keep track of where the program was while I was debugging it.

Any tips would be appreciated. Below is my code:

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 = []
    self.openlist[0].name = startcity
    self.openlist[0].path = startcity

def astar_run(self, dbg=""):
    while self.openlist:
        if self.openlist[0].name == self.goalcity:
            print self.openlist[0].path
            return self.openlist[0]
        else:
            print "Current city", self.openlist[0].name
            c2 = Roads(self.openlist[0].name)
            templist = []
            print "c2 contains", c2
            print "Templist is", templist
            x = 1
            print "Length of c2", len(c2)
            for i in range(0, len(c2)):
                print "Test point", x
                print "i value is now:", i
                print c2[i]
                templist.append(Node(c2[i]))
                templist[i].name = c2[i]
                templist[i].g = Distance(self.openlist[0].name, c2[i]) + self.openlist[0].g
                templist[i].h = Distance(c2[i], self.goalcity)
                templist[i].f = templist[i].g + templist[i].h
                templist[i].path = self.openlist[0].path + ", to " + c2[i]
                self.openlist.append(templist[i])
                print "x value is now:", x
                x = x + 1
                print self.openlist[i].name
        self.closedlist.append(self.openlist[0].name)
        del self.openlist[0]
        p = 0
        q = len(self.openlist)
        while p in range(0, q):
            print "Openlist", p, "is", self.openlist[p].name
            if self.openlist[p].name in self.closedlist:
                print "Deleting", self.openlist[p]
                del self.openlist[p]
                p = p - 1
                q = len(self.openlist)
            p = p + 1
                #print "Openlist", p, "is now", self.openlist[p].name
        print "Closedlist is", self.closedlist




def Roads(city):
    c1 = adata.roadlist(city)
    return c1

def Distance(city1, city2):
    c3 = adata.dist(city1, city2)
    return c3



class Node:
def __init__(self, path=[], f=0, g=0, h=0):
    self.path = path[:]
    self.name = []
    self.f = f
    self.g = g
    self.h = h

Also, I realize that my tabs on the def's have been lost transposing the code to this site, I apologies. However, all of them are properly tabbed in my py.

Thanks in advance!

Answer 1

thing.f and thing['f'] do different things. Use

self.openlist.sort(key=operator.attrgetter('f'))