Answer: Python Puzzler #904

The answer is A. The program prints:

6
4
2
Lift off!

Why?

The loop keeps going while count > 0. Each time round it prints count, then takes away 2. When count reaches 0, the condition is false, the loop stops, and the last line prints.

Trace table

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

count	count > 0?	new count
6	yes	4
4	yes	2
2	yes	0
0	no (stop)

The code again

count = 6
while count > 0:
    print(count)
    count = count - 2
print("Lift off!")