Answer: Python Puzzler #3934

The answer is D. The program prints:

57

This answer was checked by running the program for real.

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
21	yes	21
57	yes	57
9	no	57
31	no	57
3	no	57

The code again

numbers = [21, 57, 9, 31, 3]
biggest = 0
for n in numbers:
    if n > biggest:
        biggest = n
print(biggest)