在python中返回了错误的列表

Question

def mainCall(nodeGroup):

    maxScore = -9999999
    maxPart = []
    tempPartition = []
    tempScore = 0.0

    for j in range(2, 1+nodes/2):

        nodeGroup = chooseInitPartition(j, nodeGroup)
        tempScore, tempPartition = runKL(edgeList, nodeGroup, rounds)
        print 'temp score', tempScore
        print 'temp part', tempPartition, "\n"
        if(maxScore < tempScore):
            maxScore = tempScore
            maxPart = tempPartition
            print "max score", maxScore
            print "maxpart", maxPart, "\n"

     print 'before ret max part', maxPart
     return maxScore, maxPart

finalScore, finalPartition = mainCall(nodeGroup)

I am having a problem with the above code. Everything seems fine till the for loop ends, but after that instead of printing the maxPart value at the line print 'before ret max part' , it prints the last value of tempPartition (both represent a list of numbers). The print statements confirm that the if condition is not satisfied every time, especially the last few runs in the loop. So I don't see how the value of tempPartition is being transferred to maxPart . Please help me with this. It is driving me crazy. I am sure I am missing something simple. Thanks!

EDIT:

Adding code for runKL

def runKL(edgeList, nodeGroup, rounds):

    nodeSwap = [0]*nodes
    maxLogLScore = 0.0
    edgeListLen = len(edgeList)

    networkPartitionStore = []
    logLScores = []

    #Reset count
    count = 0

    #Start main loop
    for i in range(rounds):
        #mark all vertices as unswapped
        for j in range(len(nodeSwap)):
            nodeSwap[j] = 0


        while(count < 100):
            #Choose one edge uniformly randomly
            randNum = random.uniform(0,1)
            edge = edgeList[int(math.floor(edgeListLen*randNum))]
            node1 = int(edge[0]) - 1
            node2 = int(edge[1]) - 1

            if((nodeGroup[node1] == nodeGroup[node2]) or (nodeSwap[node1] == 1) or (nodeSwap[node2] == 1)):
                count += 1
                continue
            else:
                #swap groups among nodes
                temp = nodeGroup[node1]
                nodeGroup[node1] = nodeGroup[node2]
                nodeGroup[node2] = temp

                #mark vertices as swapped
                nodeSwap[node1] = 1
                nodeSwap[node2] = 1

                #calculate likelihood
                logLScore = logLikelihood(edgeList, nodeGroup)
                logLScores.append(logLScore)

                #store network
                networkPartitionStore.append(nodeGroup)

                #reset count value
                count = 0

        #end while loop

        #Choose the index of the maximum likelihood score
        maxLogLScore = max(logLScores)
        index = logLScores.index(maxLogLScore)
        #print 'max score', modularityScores[index]

        #Choose the corresponding network partition i.e. the way the groups have been assigned to the nodes
        nodeGroup = networkPartitionStore[index]

        #Reset partition storage list and modularity scores
        networkPartitionStore = []
        logLScores = []

        #Store initial network partition structure and modularity score. 
        networkPartitionStore.append(nodeGroup)
        logLScores.append(maxLogLScore)

    return maxLogLScore, nodeGroup

Answer 1

When you say

maxPart = tempPartition

you are not creating a copy of tempPartition but you are making the maxPart also to point to the same list that tempPartition points to. To really make a copy, you can use slicing notation like this

maxPart[:] = tempPartition

or

maxPart = tempPartition[:]

The difference between maxPart[:] = tempPartition and maxPart = tempPartition[:] is that the former mutates the maxPart and copies all the values from tempPartition to maxPart and latter creates a new list with a copy of all the data in tempPartition and makes the maxPart points to the newly created list.