Question

我需要一些Python的map函数帮助。我试图执行此代码，但我收到错误：

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这是我的确切代码，以及每个函数的输出：

infinity = 1000000
invalid_node = -1
startNode = 0

#Values to assign to each node
class Node:
     def __init__(self):
       self.distFromSource = infinity
       self.previous = invalid_node
       self.visited = False

#read in all network nodes
#node = the distance values between nodes
def network():
    f = open ('network.txt', 'r')
    theNetwork = [[int(networkNode) for networkNode in line.split(',')] for line in f.readlines()]
    #theNetwork = [[int(node) for node in line.split(',')] for line in f.readlines()]
    print theNetwork

    return theNetwork

#for each node assign default values
#populate table with default values
def populateNodeTable(): 
    nodeTable = []
    index = 0
    f = open('network.txt', 'r')
    for line in f: 
      networkNode = map(int, line.split(',')) 
      nodeTable.append(Node())

      print "The previous node is " ,nodeTable[index].previous 
      print "The distance from source is " ,nodeTable[index].distFromSource
      #print networkNode
      index +=1
    nodeTable[startNode].distFromSource = 0 

    return nodeTable

currentNode = startNode

#find the nearest neighbour to a particular node
def nearestNeighbour(currentNode, theNetwork):
     listOfNeighbours = []
     nodeIndex = 0
     for networkNode in theNetwork[currentNode]:
          if networkNode != 0 and nodeTable[nodeIndex].visited == False:
            listOfNeighbours.append(networkNode)
            nodeIndex +=1
     print "The nearest neighbours are", listOfNeighbours
##     #print node.distFromSource, node.previous, node.visited
##
     return listOfNeighbours

def tentativeDistance (theNetwork, listOfNeighbours):
    shortestPath = []
    for nodeIndex in theNetwork:
         currentDistance = listOfNeighbours[nodeIndex] + startNode
         print currentDistance
         if currentDistance[theNetwork][nodeIndex] < Node.distFromSource:
            theNetwork[node].previous = nodeIndex
            theNetwork[node].distFromSource = nodeIndex
            theNetwork[node].visited = True;
            shortestPath.append(indexNode)
            nodeIndex +=1
    print shortestPath

if __name__ == "__main__":
     nodeTable = populateNodeTable()
    #nodeTable = populateNodeTable(self)
     theNetwork = network()
     #listOfNeighbours = nearestNeighbour(currentNode, theNetwork)
     #tentativeDistance(theNetwork, listOfNeighbours)

我的网络功能输出是一个2D列表：

[[0, 2, 4, 1, 6, 0, 0], [2, 0, 0, 0, 5, 0, 0], [4, 0, 0, 0, 5, 5, 0], [1, 0, 0, 0, 1, 1, 0], [6, 5, 0, 1, 0, 5, 5], [0, 0, 5, 1, 5, 0, 0], [0, 0, 0, 0, 5, 0, 0]]

我的populateNodeTable函数的输出是：

The previous node is  -1
The distance from source is  1000000
The previous node is  -1
The distance from source is  1000000
The previous node is  -1
The distance from source is  1000000
The previous node is  -1
The distance from source is  1000000
The previous node is  -1
The distance from source is  1000000
The previous node is  -1
The distance from source is  1000000
The previous node is  -1
The distance from source is  1000000

我的网络文本文件具有此格式（减去行间距）：

0,2,4,1,6,0,0

2,0,0,0,5,0,0

4,0,0,0,5,5,0

1,0,0,0,1,1,0

6,5,0,1,0,5,5

0,0,5,1,5,0,0

0,0,0,0,5,0,0

错误是：

currentDistance = listOfNeighbours[nodeIndex] + startNode
TypeError: list indices must be integers, not list

这是我的listOfNeighbours的内容，在我的另一个函数中生成：

[2, 4, 1, 6]

我不明白这方面的Python文档，对初学者来说听起来并不容易

Answer 1

for nodeIndex in theNetwork:

不会使nodeIndex遍历theNetwork中的 indices ，而是覆盖其元素的 values 。你应该使用

for nodeIndex,node in enumerate(theNetwork):
    # theNetwork[nodeIndex] is now known as node

Answer 2

通过在控制台上打印来检查您的网络变量：

print(theNetwork)

它可以是一个列表列表，你想要它（为了使用它的各个项目作为标记）是它的一个列表。

Answer 3

listOfNeighbors是一个列表，从零开始索引。所以，listOfNeighbors [0] = 2，listOfNeighbors [1] = 4.错误告诉你nodeIndex，你用作索引来访问listOfNeighbors中的项目，是一个列表 - 不是预期的整数值。这意味着网络必须由列表组成。在为currentDistance分配值之前，您可以尝试“print nodeIndex”以查看它的组成。另外，我也看不到你在上面的函数中定义“node”或“indexNode”的位置。

另外，只是为了澄清 - 这是一个你最终将传递给地图的功能吗？我没有在函数中的任何地方看到地图调用。

Python地图功能

3 个答案: