Answer: Python Puzzler #960

The answer is B. The program prints:

[1, 4, 9, 16]

Why?

append adds one item to the end of the list each time round the loop. The loop runs for n = 1, 2, 3, 4.

Trace table

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

n	n * n	results so far
1	1	[1]
2	4	[1, 4]
3	9	[1, 4, 9]
4	16	[1, 4, 9, 16]

The code again

results = []
for n in range(1, 5):
    results.append(n * n)
print(results)