嵌套列表理解转置矩阵

Question

I just started out my journey with Python and I can't figure out how this loop transposes the matrix! Can someone give a detailed explanation?

 matrix = [ [1,2,3,4], [5,6,7,8], [9,10,11,12] ]

 [[row[i] for row in matrix] for i in range(4)]

Answer 1

Maybe it will help to write the comprehension as nested loops?

It is equivalent to:

transposed = []
for i in range(4):
    col = []
    for row in matrix:
        col.append(row[i])
    transposed.append(col)

print(transposed)