hello! this code shows how to calculate the shortest path between two cities on a map based on: http://www.python.org/doc/essays/graphs.html i have changed the code with the hlp of a news article by June Kim. For small graphs it works better than the Dijkstra algorithm. If anybody has an idea how to speed up this algorithm ? By the way I am looking forward to the second part of the essay. def weight(path): weight_of_path= 0 for node in path: weight_of_path = weight_of_path + node[1] return weight_of_path def find_shortest_path(graph, start, end, path=[]): path = path + [start] path_hlp=[] for node_hlp in path: path_hlp = path_hlp + [node_hlp[0]] if start[0] == end: return path shortest_path = None for node in graph[start[0]]: if node[0] not in path_hlp: new_path = find_shortest_path(graph, node, end, path) if new_path: if not shortest_path or weight(new_path) < weight(shortest_path): shortest_path = new_path return shortest_path # real geographic area in vienna graph = {'A':[('B',513)], 'B':[('A',513),('C',1513),('J',1684),('K',1107)], 'C':[('B',1513),('D',406),('K',654)], 'D':[('C',406),('E',834),('L',860)], 'E':[('D',834),('L',889),('F',2472)], 'F':[('E',2472),('Z',170),('M',765),('G',2796)], 'G':[('F',2796),('N',1317),('H',737)], 'H':[('G',737),('P',1181),('I',1072)], 'I':[('H',1072),('Q',1020),('J',467)], 'J':[('I',467),('Q',565),('B',1684)], 'K':[('B',1107),('C',654),('P',1340),('Q',719)], 'Q':[('K',719),('I',1020),('J',565)], 'L':[('D',860),('E',889),('M',729),('O',648)], 'O':[('L',648),('N',709),('P',153)], 'M':[('L',729),('F',765),('N',444)], 'N':[('M',444),('G',1317),('O',709)], 'P':[('O',153),('H',1181),('K',1340)], 'Z':[('F',170)]} pathfinder = find_shortest_path(graph,('A',0),'Z')