matrix multiplication without numpy

Question

#Here I should get [[1,3,4],[2,5,7],[5,9,6]] as my final output but Instead im getting [[5,9,6],[5,9,6],[5,9,6]]

def matrix_mul(A, B):
    m1 = len(A) 
    n1 = len(A[0])
    m2 = len(B)
    n2 = len(B[0])
    if(n1!=m2):
        print("Not Possible")
    else:
        c = [[0]*n2]*m1
        for i in range(m1):
            for j in range(n2):
                total = 0
                for k in range(n1):
                    total += A[i][k] * B[k][j]
                c[i][j]=total
        return c
A = [[1,3,4],[2,5,7],[5,9,6]]
B = [[1,0,0],[0,1,0],[0,0,1]]    
print("AxB\n",matrix_mul(A, B))

[Related](https://stackoverflow.com/questions/2612802/list-changes-unexpectedly-after-assignment-how-do-i-clone-or-copy-it-to-prevent) — hilberts_drinking_problem, Nov 24 '20 at 08:56
the problem is `c = [[0]*n2]*m1` it creates `m1` copies of an identical list, you modify one you modify them all — rioV8, Nov 24 '20 at 09:04
@lorenzozane I was referring to the copy vs. reference issue, which rioV8 spelled out. — hilberts_drinking_problem, Nov 24 '20 at 09:06

score 3 · Accepted Answer · answered Nov 24 '20 at 09:05

3

Change c = [[0]*n2]*m1 to

c = [[0]*n2 for _ in range(m1)]

answered Nov 24 '20 at 09:05

rioV8

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matrix multiplication without numpy

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