用python实现一个基于栅格地图的astar

算法，你能给出代码示例吗？

当然可以，以下是一个基于栅格地图的A*算法的Python代码示例：

import heapq

class Grid:
    def __init__(self, width, height):
        self.width = width
        self.height = height
        self.walls = set()

    def in_bounds(self, pos):
        x, y = pos
        return 0 <= x < self.width and 0 <= y < self.height

    def passable(self, pos):
        return pos not in self.walls

    def neighbors(self, pos):
        x, y = pos
        results = [(x+1, y), (x, y-1), (x-1, y), (x, y+1)]
        if (x + y) % 2 == 0: results.reverse() # aesthetics
        results = filter(self.in_bounds, results)
        results = filter(self.passable, results)
        return results

    def cost(self, current, next):
        return 1

def heuristic(a, b):
    return abs(a[0] - b[0]) + abs(a[1] - b[1])

def astar(graph, start, goal):
    frontier = []
    heapq.heappush(frontier, (0, start))
    came_from = {}
    cost_so_far = {}
    came_from[start] = None
    cost_so_far[start] = 0

    while frontier:
        current = heapq.heappop(frontier)[1]

        if current == goal:
            break

        for next in graph.neighbors(current):
            new_cost = cost_so_far[current] + graph.cost(current, next)
            if next not in cost_so_far or new_cost < cost_so_far[next]:
                cost_so_far[next] = new_cost
                priority = new_cost + heuristic(goal, next)
                heapq.heappush(frontier, (priority, next))
                came_from[next] = current

    return came_from, cost_so_far

这个代码示例实现了一个基于栅格地图的A*算法，其中Grid类表示地图，heuristic函数表示启发式函数，astar函数表示A*算法的实现。你可以根据自己的需求进行修改和扩展。