Answer: Python Puzzler #1707

The answer is B. The program prints:

31

Why?

The loop remembers the biggest number it has seen so far, and replaces it whenever it finds a bigger one. This is how computers find the maximum.

Trace table

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

n	n > biggest?	biggest
19	yes	19
1	no	19
10	no	19
31	yes	31
12	no	31

The code again

numbers = [19, 1, 10, 31, 12]
biggest = 0
for n in numbers:
    if n > biggest:
        biggest = n
print(biggest)