Answer: Python Puzzler #1450

The answer is C. The program prints:

3
6
9
12

Why?

% gives the remainder after dividing. A remainder of 0 means the number divides exactly by 3, so the program prints the multiples of 3 up to 12.

Trace table

A trace table follows the program step by step. Here’s this one:

number	number % 3	printed?
1	1
2	2
3	0	yes
4	1
5	2
6	0	yes
7	1
8	2
9	0	yes
10	1
11	2
12	0	yes

The code again

for number in range(1, 13):
    if number % 3 == 0:
        print(number)