A* pathfinding over any arbitrary graph structure, with example Cartesian grid implementation

astar.py

class AStar(object):
    def __init__(self, graph):
        self.graph = graph
        
    def heuristic(self, node, start, end):
        raise NotImplementedError
        
    def search(self, start, end):
        openset = set()
        closedset = set()
        current = start
        openset.add(current)
        while openset:
            current = min(openset, key=lambda o:o.g + o.h)
            if current == end:
                path = []
                while current.parent:
                    path.append(current)
                    current = current.parent
                path.append(current)
                return path[::-1]
            openset.remove(current)
            closedset.add(current)
            for node in self.graph[current]:
                if node in closedset:
                    continue
                if node in openset:
                    new_g = current.g + current.move_cost(node)
                    if node.g > new_g:
                        node.g = new_g
                        node.parent = current
                else:
                    node.g = current.g + current.move_cost(node)
                    node.h = self.heuristic(node, start, end)
                    node.parent = current
                    openset.add(node)
        return None


class AStarNode(object):
    def __init__(self):
        self.g = 0
        self.h = 0
        self.parent = None
        
    def move_cost(self, other):
        raise NotImplementedError

astar_grid.py

from astar import AStar, AStarNode
from math import sqrt


class AStarGrid(AStar):
    def heuristic(self, node, start, end):
        return sqrt((end.x - node.x)**2 + (end.y - node.y)**2)


class AStarGridNode(AStarNode):
    def __init__(self, x, y):
        self.x, self.y = x, y
        super(AStarGridNode, self).__init__()

    def move_cost(self, other):
        diagonal = abs(self.x - other.x) == 1 and abs(self.y - other.y) == 1
        return 14 if diagonal else 10

example_grid.py

from astar_grid import AStarGrid, AStarGridNode
from itertools import product


def make_graph(width, height):
    nodes = [[AStarGridNode(x, y) for y in range(height)] for x in range(width)]
    graph = {}
    for x, y in product(range(width), range(height)):
        node = nodes[x][y]
        graph[node] = []
        for i, j in product([-1, 0, 1], [-1, 0, 1]):
            if not (0 <= x + i < width):
                continue
            if not (0 <= y + j < height):
                continue
            graph[nodes[x][y]].append(nodes[x+i][y+j])
    return graph, nodes

graph, nodes = make_graph(8, 8)
paths = AStarGrid(graph)
start, end = nodes[1][1], nodes[5][7]
path = paths.search(start, end)
if path is None:
    print "No path found"
else:
    print "Path found:", path

LICENSE

Copyright (C) 2012 Justin Poliey <justin.d.poliey@gmail.com>

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

i made the bugfix that vindolin suggested as well as improved pretty printing and added an obstacle to the gridworld example in my fork: https://gist.github.com/benaxelrod/57dd9202a93e8295c2c1

It always returns "No path found" for me. and it doesn't go inside the for loop- "for node in self.graph[current]: " (checked)
What may be the reason..

Damn, these are the prettiest lines of code that I've seen in a long time.

Great work!

hm, does it affect the results at all that you say each node is adjacent to itself?