python嵌套列表遍历问题

Question

matrix = [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]] 
matrix_1 = [[row[i] for row in matrix] for i in range(4)]
print(matrix_1)

请问各位，matrix_1的循环执行顺序是怎样的呢？初学python不太了解，感谢教导

Answer 1

matrix_1 = [[row[i] for row in matrix] for i in range(4)]
range(4) 从0到3循环四次
i = 0 → [1 5 9]
i = 1 → [2 6 10]
i = 2 → [3 7 11]
i = 3 → [4 8 12]
然后赋值给matrix_1
print(matrix_1)
输出结果如图：

希望对题主有所帮助，望采纳！！