Question

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.

Answer 1

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.