In this Decode The Code challenge, we explore the expression a, b = b, a, a powerful and concise method in Python for swapping the values of two variables. But how does this work, and why does a not get assigned to b first, followed by b being reassigned to the new value of a (effectively assigning b to itself again)?

Why It Works

The magic behind a, b = b, a lies in Python’s handling of tuple Packing And Unpacking In Python. When you write a, b = b, a, Python internally performs the following steps:

1. Tuple Packing: The right-hand side of the assignment b, a is evaluated first. This creates a temporary tuple containing the current values of b and a.

2. Tuple Unpacking: The left-hand side a, b is then assigned the values from the temporary tuple. This means a is assigned the value of b, and b is assigned the value of a.

This process of packing and unpacking ensures that both variables are updated simultaneously, preventing any overwriting of values during the swap.