How can I correct the error ' AttributeError: 'dict_keys' object has no attribute 'remove' '?

问题:

I was trying shortest path finder using dijkstra algorithm but It seems not working. Can't figure out what the problem is. Here are the code and the error message. (I'm working on Python 3.5. https://www.youtube.com/watch?v=LHCVNtxb4ss)

graph = {     'A': {'B': 10, 'D': 4, 'F': 10},     'B': {'E': 5, 'J': 10, 'I': 17},     'C': {'A': 4, 'D': 10, 'E': 16},     'D': {'F': 12, 'G': 21},     'E': {'G': 4},     'F': {'E': 3},     'G': {'J': 3},     'H': {'G': 3, 'J': 3},     'I': {},     'J': {'I': 8}, }  def dijkstra(graph, start, end):     D = {}     P = {}     for node in graph.keys():         D[node]= -1         P[node]=""     D[start]=0     unseen_nodes=graph.keys()     while len(unseen_nodes) > 0:         shortest=None         node=' '         for temp_node in unseen_nodes:             if shortest==None:                 shortest = D[temp_node]                 node = temp_node             elif D[temp_node]<shortest:                     shortest=D[temp_node]                     node=temp_node         unseen_nodes.remove(node)         for child_node, child_value in graph[node].items():             if D[child_node] < D[node] + child_value:                 D[child_node] = D[node] + child_value                 P[child_node]=node     path = []     node = end     while not (node==start):         if path.count(node)==0:             path.insert(0, node)             node=P[node]         else:             break     path.insert(0, start)     return path 

AttributeError: 'dict_keys' object has no attribute 'remove'

回答1:

In Python 3, dict.keys() returns a dict_keys object (a view of the dictionary) which does not have remove method; unlike Python 2, where dict.keys() returns a list object.

>>> graph = {'a': []} >>> keys = graph.keys() >>> keys dict_keys(['a']) >>> keys.remove('a') Traceback (most recent call last):   File "<stdin>", line 1, in <module> AttributeError: 'dict_keys' object has no attribute 'remove' 

You can use list(..) to get a keys list:

>>> keys = list(graph) >>> keys ['a'] >>> keys.remove('a') >>> keys [] 

---

unseen_nodes = graph.keys() 

to

unseen_nodes = list(graph) 

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