Question

我是Python的初学者，并且已经面临这个问题一段时间了。任何纠正问题的建议都是有价值的。下面是使用Dijkstra算法找到最短路径的代码。我有成本矩阵和源作为输入。

def dijkstra(cost_matrix,source):
    n = 20
    dist = [0 for row in range(20)]
    visited = [0 for row in range(20)]
    for j in range(20):
        visited[j] = "False"
    visited[source] = "True"
    for i in range(20):
        dist[i] = cost_matrix[source][i]
    prev_min = source
    for k in range(20):
        minimum = min(dist)
        minimum2 = min(minimum,n)
        for i in range(20):
            if dist[i] > (cost_matrix[prev_min][minimum2] + cost_matrix[minimum2][i]):
                dist[i] = cost_matrix[prev_min][minimum2] + cost_matrix[minimum2][i]
        visited[minimum2] = "True"
        prev_min = minimum2
    return dist

计算cost_matrix的代码

def matrix():
    k = 30
    b_ij = [[0 for row in range(20)] for col in range(20)]
    a_ij = [[0 for row in range(20)] for col in range(20)]
    cost_matrix = [[0 for row in range(20)] for col in range(20)]
    for i in range(20):
        for j in range(20):
            rand = random.randint(0,8)
            b_ij[i][j] = rand
            b_ij[j][i] = rand
    while(k > 0):
        rand1 = random.randint(0,19)
        rand2 = random.randint(0,19)
        a_ij[rand1][rand2] = 200
        a_ij[rand2][rand1] = 200
        k = k - 1
    for i in range(20):
        for j in range(20):
            if a_ij[i][j] != 200:
                rand = random.randint(0,8)
                a_ij[i][j] = rand
                a_ij[j][i] = rand
    for i in range(len(a_ij)):
        for j in range(len(b_ij[0])):
            for k in range(len(b_ij)):
                cost_matrix[i][j] += a_ij[i][k] * b_ij [k][j]

错误讯息：

Traceback (most recent call last):
  File "ass1.py", line 60, in <module>
    print(dijkstra(cost_matrix, 1))
  File "ass1.py", line 45, in dijkstra
    dist[i] = cost_matrix[source][i]
TypeError: 'NoneType' object is not subscriptable

Answer 1

您仍然没有在创建cost_matrix的位置发布实际代码。您发布了矩阵函数的代码，但没有发布使用矩阵函数的代码。

但是，看起来问题是你的matrix函数没有返回任何内容。它只是创建一个矩阵并抛弃它。您需要在该函数的末尾添加return cost_matrix。

Answer 2

cost_matrix或cost_matrix [source]的值为None，但它应该是一个列表。

在行前打印它们：

dist[i] = cost_matrix[source][i]

找出问题所在。

顺便说一句，你应该把numpy用于这类东西。

Python - ＆＃39; NoneType＆＃39;对象不是可订阅的错误

2 个答案: