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):
        # NOTE: this is traditionally sqrt((end.x - node.x)**2 + (end.y - node.y)**2)
        # However, if you are not interested in the *actual* cost, but only relative cost,
        # then the math can be simplified.
        return abs(end.x - node.x) + abs(end.y - node.y)
        #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

    def __repr__(self):
        return '(%d %d)' % (self.x, self.y)

example_grid.py

#! /usr/bin/env python

from astar_grid import AStarGrid, AStarGridNode
from itertools import product

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

graph, nodes = make_graph({"width": 8, "height": 8, "obstacle": [[2,5],[3,5],[4,5],[5,5]]})
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.

Can you please tell me how to replace the start and end with user defined coordinates.
I gave "start, end = (x1, y1), (x2, y2)" but it returns "no path found"

@KasunRama: Because you're calling an AStarGrid object when doing the search, the inputs must be AStarGridNode objects as defined in astar_grid.py. The example grid of AStarGridNode objects you're looking for is created on line 7 of example_grid.py.

Your custom start and end points should be written as:
start, end = nodes[x1][y1], nodes[x2][y2]

I don't fully agree with your comment about changing the heuristic. You changed the Euclidean distance to the Manhattan distance. If you are truely interested in the Euclidean distance, but only care about the rank (relative distance) the formula should be (end.x - node.x)**2 + (end.y - node.y)**2.