Python不会运行程序

Question

我对python不熟悉，但有C和Matlab的大学经验。我试图编写并运行dijkstras算法，但是当我运行它时，什么也没有发生。我会附上代码（包括注释掉失败的尝试），希望有人能引导我朝正确的方向前进。在

#must write script to turn matrix into this form of graph
graph = {'a':{'c':3,'e':5},'c':{'a':3,'d':5},'d':{'c':3,'e':6},'e':
{'d':6,'a':5}}
unseenNodes = {}
goal = {}
start = {}


#defining function
def dijkstra(graph, start, goal):
    shortest_distance = {} #empty dictionary
    predeccesor = {} #empty dictionary 
    unseenNodes = graph #makes it run through til all are seen
    path = []
def __init__(self):  
 #start node to next node
    print( str("hi"))

     for node in unseenNodes:
        shortest_distance[node]=9999999
        shortest_distance[start]=0
        print(shortest_distance)

#beefy bit of dijkstras alogrithim 
    while unseenNodes:
        minNode=None
        for node in unseenNodes:
            if minNode is None:
                minNode = node

            elif shortest_distance[node] < shortest_distance[minNode]:
                minNode = node

            for childNode, weight in graph [minNode].items():
                if weight + shortest_distance[minNode] < 
 shortest_distance[childNode]:
                    shortest_distance[childNode] = weight + shortest_distance[minNode]

                predeccesor[childNode] = minNode
                unseenNodes.pop(minNode)

                print(shortest_distance)

#reverse stack approach to trace path
    currentNode = goal
    while currentNode != start:
        try:
            path.insert(0,currentNode)
            currentNode = predeccesor[currentNode]
         except KeyError:
            print('path not valid')
        #break

        path.insert(0,start)
        if shortest_distance[goal] != infinity:
            #print(goal) 
            print('shortest distance is' + str(shortest_distance[goal]))
            print('path is' + str(path))
         else:
             Print('Something Went Wrong!')

#break

dijkstra(graph, 'a', 'd')

Answer 1

你只需要一次改变

• 从代码中删除def __init__(self): function。在

• 类中使用初始化函数来初始化 对象变量。

• 不能调用__init__函数，这就是为什么没有得到任何输出。

• 另外，适当地进行缩进，你就会得到你的输出。在

Answer 2

好的，所以我修复了一堆代码的缩进、作用域和名称问题（见下文），得到了以下错误

hi
{'a': 0}
{'a': 0, 'c': 9999999}
{'a': 0, 'c': 9999999, 'd': 9999999}
{'a': 0, 'c': 9999999, 'd': 9999999, 'e': 9999999}
{'a': 0, 'c': 3, 'd': 9999999, 'e': 9999999}
Traceback (most recent call last):
  File "dijkstras.py", line 69, in <module>
    dijkstra(graph, 'a', 'd')
  File "dijkstras.py", line 47, in dijkstra
    unseen_nodes.pop(minNode)
KeyError: 'a'

也许这能帮你继续吗？在

^{pr2}$

Answer 3

dijkstra函数只执行这四行代码，因为在定义第二个函数之前，它们是惟一的代码行。因此，当您最后调用此函数时，程序会创建一些空字典，然后关闭：

shortest_distance = {} #empty dictionary
predeccesor = {} #empty dictionary 
unseenNodes = graph #makes it run through til all are seen
path = []

您定义的第二个函数，init（）是一个类方法，不能在类之外定义它。在

先看看python中的一些更基本的算法，然后熟悉语法（我不知道它与C有多大的不同）。在