[[row[i] for row in matrix] for i in range(4)] 执行顺讯

这个表达式会先执行 range(4)，得到一个包含 0 到 3 的整数的列表，然后对于每个整数 i，会执行一个列表推导式 [row[i] for row in matrix]，其中 matrix 是一个二维列表。该推导式会遍历 matrix 的每一行，并取出第 i 个元素，将这些元素组成一个新的列表。最终，该表达式会得到一个包含 4 个元素的列表，每个元素是 matrix 对应列的元素组成的列表。

相关问题

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

As an AI language model, I can explain how this code works and provide an example output.

This code is using a list comprehension to create a new matrix that is transposed from the original matrix. The original matrix is assumed to be a 4x4 matrix.

Here's how the code works:

- The outer list comprehension creates a new list that contains 4 nested lists. Each nested list will represent a row in the transposed matrix.
- The inner list comprehension loops through each row in the original matrix and extracts the corresponding element in the i-th column. This element is then added to the i-th nested list in the new matrix.

Here's an example of this code in action:

matrix = [[1, 2, 3, 4],
          [5, 6, 7, 8],
          [9, 10, 11, 12],
          [13, 14, 15, 16]]

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

print(transposed)

Output:

[[1, 5, 9, 13],
 [2, 6, 10, 14],
 [3, 7, 11, 15],
 [4, 8, 12, 16]]

As you can see, the transposed matrix has the rows and columns flipped from the original matrix. The first row of the transposed matrix contains the first column of the original matrix, and so on.

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

这段代码有误，应该是：

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

它的作用是将一个 $3 \times 4$ 的矩阵转置成一个 $4 \times 3$ 的矩阵，具体来说，它的输出结果是：

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

其中，第 $i$ 行第 $j$ 列的元素是原矩阵中第 $j$ 行第 $i$ 列的元素。