NoneType 对象不可迭代错误

Question

我的任务是为 Dijkstra 算法编写 classes。尽管不允许我编辑 Dijkstra class:

class Dijkstra():
# initialize with a string containing the root and a
# weighted edge list
def __init__(self, in_string):
    self.root, self.nnodes, self.adj_list = self.convert_to_adj_list(in_string)
    self.nodes = [Node(i) for i in range(self.nnodes)]
    self.nodes[self.root].key = 0
    self.heap = MinHeap(self.nodes)
# the input is expected to be a string 
# consisting of the number of nodes
# and a root followed by 
# vertex pairs with a non-negative weight
def convert_to_adj_list(self, in_string):
    nnodes, root, edges = in_string.split(';')
    root = int(root)
    nnodes = int(nnodes)
    adj_list = {}
    edges = [ map(int,wedge.split()) for wedge in edges.split(',')]
    for u,v,w in edges:
        (adj_list.setdefault(u,[])).append((v,w))
    for u in range(nnodes):
        adj_list.setdefault(u,[])

这是我的问题：

string = '3; 0; 1 2 8, 2 0 5, 1 0 8, 2 1 3'
print(Dijkstra(string))
Traceback (most recent call last):
  File "<pyshell#321>", line 1, in <module>
    print(Dijkstra(string))
  File "C:\Users\TheDude\Downloads\dijkstra.py", line 71, in __init__
    self.root, self.nnodes, self.adj_list = self.convert_to_adj_list(in_string)
TypeError: 'NoneType' object is not iterable

我要分配 append 的 return 值吗？我该如何解决 w/o 编辑 class Djikstra() 阅读坦克。

Answer 1

为了作业

    self.root, self.nnodes, self.adj_list = self.convert_to_adj_list(in_string)

为了工作，convert_to_adj_list 必须 return 一个包含三个值的元组被解压到这三个变量中。但是，您的方法 return 什么都没有（因此隐式地 returning None）。将您的 convert_to_adj_list 方法更改为类似这样的方法，然后它应该可以工作：

def convert_to_adj_list(self, in_string):
    ... your code ...
    return root, nnodes, adj_list

NoneType 对象不可迭代错误

NoneType object is not iterable Error

python

append

iterable

nonetype