在Python中打印二维列表的列 [英] Printing a column of a 2-D List in Python

问题描述

假设A = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

然后A[0][:]打印[1, 2, 3]

但是为什么A[:][0]再次打印[1, 2, 3]?

But why does A[:][0] print [1, 2, 3] again ?

它应该打印列[1, 4, 7]，不是吗?

It should print the column [1, 4, 7], shouldn't it?

推荐答案

[:]等同于复制.

A[:][0]是A副本的第一行. A[0][:]是A的第一行的副本.

A[:][0] is the first row of a copy of A. A[0][:] is a copy of the first row of A.

两者是相同的.

要获取第一列:[a[0] for a in A] 或使用numpy和np.array(A)[:,0]

To get the first column: [a[0] for a in A] Or use numpy and np.array(A)[:,0]

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