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我有任務爲Dijkstra的算法編寫類。雖然我不能編輯的Dijkstra類:NoneType對象不可迭代錯誤
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,[])
這是我的問題:
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
難道我給你append
的返回值?我該如何解決它不W/o編輯 class Djikstra()
坦克供閱讀。
'convert_to_adj_list'回報'None',因爲你沒有用一個return語句爲它供給。 – miradulo
你應該從'convert_to_adj_list'得到一個返回值,所以將'return adj_list'添加到'convert_to_adj_list'定義的末尾。 –
所以如果我不設置返回值,任何函數都會返回None? 我必須使用Dijkstra類,所以我需要聯繫老師來解決這個問題。 – TheDude