Answer: Python Puzzler #1360

The answer is B. The program prints:

Checked by running the program for real.

Python works from the inside out. First double(6) returns 12. Then that answer goes into double again, which returns 24.

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

step	value
double(6)	12
double(12)	24

def double(number):
    return number * 2

print(double(double(6)))

Try it: change one number in the program and predict the new output before you run it.