Answer: Python Puzzler #1829

The answer is B. The program prints:

37

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
31	yes	31
28	no	31
37	yes	37
15	no	37
18	no	37

The code again

numbers = [31, 28, 37, 15, 18]
biggest = 0
for n in numbers:
    if n > biggest:
        biggest = n
print(biggest)