Tuple Unpacking

Note

Source: Python-specific — no direct equivalent in the C# edition. The swap a, b = b, a replaces the three-variable swap used in the C# sorting examples. zip() unpacking replaces paired index loops.

Tuple unpacking (also called destructuring) assigns each element of a tuple to a separate variable in one statement.

Basic Unpacking

point = (3, 7)
x, y = point
print(x, y)

Output:

3 7

The number of variables on the left must match the number of elements in the tuple (or you get a ValueError).

Swapping Variables

The cleanest way to swap two variables in Python uses tuple unpacking:

a, b = 10, 20
a, b = b, a
print(a, b)

Output:

20 10

Python evaluates the right-hand side completely before assigning, so no temporary variable is needed. Compare this to the C# equivalent:

int t = a;
a = b;
b = t;

Unpacking Function Return Values

A function can return multiple values as a tuple, and the caller can unpack them:

def min_max(nums):
    return min(nums), max(nums)

lo, hi = min_max([3, 1, 4, 1, 5, 9])
print(lo, hi)

Output:

1 9

Unpacking in for Loops with zip()

zip(a, b) pairs up elements from two sequences. Unpacking in the for heading processes both at once:

names = ["Alice", "Bob", "Carol"]
scores = [88, 73, 95]

for name, score in zip(names, scores):
    print(f"{name}: {score}")

Output:

Alice: 88
Bob: 73
Carol: 95

zip() stops at the shortest sequence. Use zip(strict=True) in Python 3.10+ to raise an error if the sequences have different lengths.

Extended Unpacking

A * prefix captures the “rest” of the sequence into a list:

first, *rest = [1, 2, 3, 4, 5]
print(first)   # 1
print(rest)    # [2, 3, 4, 5]

*body, last = [1, 2, 3, 4, 5]
print(body)    # [1, 2, 3, 4]
print(last)    # 5