The answer is A. The program prints:
8 12
Why?
Python works out everything on the right first, using the old values: b is 8 and a + b is 12. Then it puts them into a and b at the same time.
Trace table
A trace table follows the program step by step. Here’s this one:
| a | b | |
|---|---|---|
| before | 4 | 8 |
| after | 8 | 12 |
The code again
a = 4
b = 8
a, b = b, a + b
print(a, b)Try it: change one number in the program and predict the new output before you run it.