CODEWITHSUNDEEP
python
Lilluda 5
Lilluda 5

Reputation: 1109

Python List Values being assigned to each other

I'm having a problem writing the following code: 

D = [
        [0,3,8,999,-4],
        [999,0,999,1,7],
        [999,4,0,999,999],
        [2,999,-5,0,999],
        [999,999,999,6,0]
    ]

def FloydWarshall (W):
    matrices = [W[:]]
    pred = [W[:]]

    print (matrices is pred)
    print (pred is matrices)
    print (pred is W)
    print (matrices is W)

    for i in range(0,len(pred[0])):
        for j in range(len(pred[0][i])):

            if pred[0][i][j] != 999 and pred[0][i][j] != 0:
                pred[0][i][j] = i +1
            else:
                pred[0][i][j] = False 

    return (matrices,pred)
FloydWarshall(D)

the values that are being returned are the exact same matrices, why is this? The print statement say that they are not pointers to the same spot in memory, correct?

Upvotes: 0

Views: 62

Answers (1)

jamylak
jamylak

Reputation: 133554

You are only making a shallow copy of the nested lists, so mutating them will still affect both matrices. You might want to use copy.deepcopy

Upvotes: 5

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