过滤奇数
M = [[1,2,3],
[4,5,6],
[7,8,9]]
col2 = [row[1] + 1 for row in M if row[1] % 2 == 0]
print (col2)
输出：[3, 9]
我希望它能过滤掉奇数，但它的作用恰恰相反。
M = [[1,2,3],
[4,5,6],
[7,8,9]]
col2 = [row[1] + 1 for row in M if row[1] % 2 == 0]
print (col2)
Output: [3, 9]
I'm expecting it to filter out the odd numbers, but it does the opposite.
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评论（4）
该代码所做的正是您所期望的 - 如果第二项是偶数，则将其加一并将其放入列表中。
因此，对于第一行，它认为 2 % 2 == 0 为 True，并设置 col2[0] = 2 + 1 = 3。对于第二行，5 % 2 == 0 为 False。对于第三行，8%2 == 0 为 True，并且 col2[1] = 8 + 1 = 9。
The code is doing exactly what you would expect - if the second item is even, increase it by one and put it into the list.
So for the first row, it sees that 2 % 2 == 0 is True, and sets col2[0] = 2 + 1 = 3. For the second row, 5 % 2 == 0 is False. For the third row, 8%2 == 0 is True, and col2[1] = 8 + 1 = 9.
我相信您需要将比较从
== 0切换到== 1。任何数除以2的模都是0或1，奇数时为1。
I believe you need to switch the comparison to
== 1from== 0.The modulus of any number divided by 2 is 0 or 1, 1 when it is odd.
您正在测试
row[1]%2，但正在打印row[1]+1因此，当
row[1]==2时，它是偶数，但您要将3附加到结果当
row[1]==5时，它是奇数，所以你将其过滤掉当
row[1]==8时，它是偶数，但您将9附加到结果中You are testing
row[1]%2, but printingrow[1]+1so when
row[1]==2, it is even, but you are appending3to the resultwhen
row[1]==5, it is odd, so you filter it outand when
row[1]==8, it is even, but you are appending9to the result