如何删除python

Question

我正在尝试在python3中编写算法dijkstra，我想我已经与python 2和python 3混淆了。我想删除unseen_node。代码如下所示

D={}
P={}

for node in graph.keys():
    D[node] = -1
    P[node] = ""
D[start] = 0
unseen_nodes = graph.keys()  #graph is a dict
while len(unseen_nodes)>0:
    shortest = None
    node = ''

    for temp_node in unseen_nodes:
        if shortest == None:
            shortest = D[temp_node]
        elif(D[temp_node]<shortest):
            shortest = D[temp_node]
            node=temp_node

    unseen_nodes.remove(node) #gives an AttributeError:
                              'dict_keys' object has no attribute'remove'