a = [1, 2, 3] b = [10, 20] a = a + b # Create a new list a+b and assign back to a. print a # [1, 2, 3, 10, 20] # Equivalently: a = [1, 2, 3] b = [10, 20] a += b print a # [1, 2, 3, 10, 20]