使用python在DFS（深度优先搜索）中导入动态文件

Question

我想使用DFS算法，并尝试导入文件。我有一个文件的开头和结尾（如下），但是这里有很多问题

1。查找动态图 2.无法正确打印

class Graph:
    file = open("input4.txt","r") #import file here
    lines = file.readlines()

    #find graph for DFS

    start_vertex = []
    end_vertex = []

    for line in lines:
            start_vertex.append(line[0])
            end_vertex.append(line[1])

            graph = {}
    for i in range(len(lines)):
            v = start_vertex[i]
    if v in graph:
            graph[v] |= set([end_vertex[i]])
    else:
            graph[v] = set([end_vertex[i]])

    #dfs code

    def dfs(graph, start, visited = None):
            if visited is None:
                    visited = set()
                    visited.add(start)
                    print(start)
            for next in graph[start] - visited:
                    dfs(graph, next, visited)
            return visited

g=Graph()
#print my file
filename = open('input4.txt', 'r')  
for line in filename:
node1, node2, d = line.split()
newnode1=sorted(node1) #sort my node
if node1!="END" and node2!="OF": 
    print(node1)
g.dfs('S') #here is the problem

我的文件input4.txt

first column is start;second is end; third is weight
S V1 3
S V2 2
V1 V3 1
V1 V4 1
V2 V4 1
V2 V6 2
V3 V5 2
V3 V7 3
V4 V7 2
V5 V9 2
V6 V8 4
V7 V9 5
V7 V10 1
V8 V10 3
V8 T 5
V9 V11 3
V10 V13 3
V11 V12 1
V12 T 2
V13 T 9

但显示：TypeError：“ Graph”对象不可下标 我该怎么办？ 谢谢你