如何解决dfs、bfs中的KeyError

Question

I was trying to create bfs, dfs programs by using the following python code. Unfortunately having this error...... anybody plz help for me

Traceback (most recent call last): File "D:...\1260.py", line 35, in print(dfs(graph, 1)) File "D:...\1260.py", line 30, in dfs stack.extend(graph[node]) KeyError: 4

graph = {
    1: [2, 3, 4],
    2: [4],
    3: [4]
}

def bfs(graph, start_node):
    visit = list()
    queue = list()

    queue.append(start_node)
    while queue:
        node = queue.pop(0)
        if node not in visit:
            visit.append(node)
            queue.extend(graph[node])
            
    return visit

def dfs(graph, start_node):
    visit = list()
    stack = list()

    stack.append(start_node)

    while stack:
        node = stack.pop()
        if node not in visit:
            visit.append(node)
            stack.extend(graph[node])

    return visit

if '__main__' == __name__:
    print(dfs(graph, 1))
    print(bfs(graph, 1))

Answer 1

stack.extend(graph[node])

You have no node key in the graph .

try:
    stack.extend(graph[node])
except KeyError:
    print(f"Unexpected node: {node}")