def aStarAlgo(start_node, stop_node):
    open_set = set(start_node)
    closed_set = set()
    g = {}
    parents = {}

    g[start_node] = 0

    parents[start_node] = start_node

    while len(open_set) > 0:
        n = None

        for v in open_set:
            if n is None or g[v] + heuristic(v) < g[n] + heuristic(n):
                n = v

        if n == stop_node or Graph_nodes[n] is None:
            pass
        else:
            for (m, weight) in get_neighbors(n):

                if m not in open_set and m not in closed_set:
                    open_set.add(m)
                    parents[m] = n
                    g[m] = g[n] + weight


                else:
                    if g[m] > g[n] + weight:

                        g[m] = g[n] + weight

                        parents[m] = n


                        if m in closed_set:
                            closed_set.remove(m)
                            open_set.add(m)

        if n is None:
            print('Path does not exist!')
            return None


        if n == stop_node:
            path = []

            while parents[n] != n:
                path.append(n)
                n = parents[n]

            path.append(start_node)

            path.reverse()

            print('Path found: {}'.format(path))
            return path


        open_set.remove(n)
        closed_set.add(n)

    print('Path does not exist!')
    return None



def get_neighbors(v):
    if v in Graph_nodes:
        return Graph_nodes[v]
    else:
        return None



def heuristic(n):
    H_dist = {
        'A': 11,
        'B': 6,
        'C': 99,
        'D': 1,
        'E': 7,
        'G': 0,

    }

    return H_dist[n]


Graph_nodes = {
    'A': [('B', 2), ('E', 3)],
    'B': [('C', 1), ('G', 9)],
    'C': None,
    'E': [('D', 6)],
    'D': [('G', 1)],

}

aStarAlgo('A', 'G')