如何在没有返回或中断Python的情况下中断函数

2019年8月3日 159次阅读

我是在节点a和b之间遍历的dfs,但是当我在节点b处断开循环时,算法继续.这是我的代码：

import networkx as nx

def Graph():
    G=nx.Graph()

    k = 30

    G.add_edge(1,2)
    G.add_edge(2,3)
    G.add_edge(1,3)

    for i in range(2,k+1):
        G.add_edge(2*i-2,2*i)
        G.add_edge(2*i-1,2*i)
        G.add_edge(2*i-1,2*i+1)
        G.add_edge(2*i,2*i+1)

    G.add_nodes_from(G.nodes(), color='never coloured')
    G.add_nodes_from(G.nodes(), label = -1)
    G.add_nodes_from(G.nodes(), visited = 'no')

    return G

def dfs(G,a,b,u):
    global i
    G.node[u]['visited'] = 'yes'
    i += 1
    G.node[u]['label'] = i
    print(u)
    print("i", i)
    for v in G.neighbors(u):
        if v == b:
            G.node[v]['visited'] = 'yes'
            i += 1
            G.node[v]['label'] = i
            print("b is ", v)
            print("distance from a to b is ", G.node[v]['label'])
            break### the problem area, doesn't break out the function
        elif v != b:
            if G.node[v]['visited'] == 'no':
                dfs(G,a,b,v)
G=Graph()
a=1
b=19
i = 0
print('Depth-First-Search visited the following nodes of G in this order:')
dfs(G,a,b,a)  ### count the DFS-path from a to b, starting at a
print('Depth-First Search found in G7 a path between vertices', a, 'and', b, 'of length:', G7.node[b]['label'])
print()

我已经尝试退出for循环,尝试使用break并尝试使用try / catch方法.是否有任何优雅的方式来突破这个功能,还是我必须重写它,因为它没有通过你的所有邻居递归？

最佳答案 这里的问题不是中断或返回,而是你使用递归而不是在每次递归调用中停止循环.你需要做的是从你的dfs函数返回一个结果,告诉你是否找到了你的节点,然后如果递归调用确实找到它,则打破你的else块中的循环.像这样的东西：

def dfs(G,a,b,u):
    global i
    G.node[u]['visited'] = 'yes'
    i += 1
    G.node[u]['label'] = i
    print(u)
    print("i", i)
    for v in G.neighbors(u):
        if v == b:
            G.node[v]['visited'] = 'yes'
            i += 1
            G.node[v]['label'] = i
            print("b is ", v)
            print("distance from a to b is ", G.node[v]['label'])
            return True
        elif v != b:
            if G.node[v]['visited'] == 'no':
                found = dfs(G,a,b,v)
                if found:
                    return True
    return False

请注意这是如何通过整个调用堆栈将成功结果传播回来的.

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