feature_02_extended_unpacking.md

2. Extended Unpacking

Concept summary

Extended unpacking lets you split a sequence into head, middle, and tail in one statement. The starred target (*middle) captures all remaining elements as a list.

What C# developers usually expect

In C#, this usually needs index access, slicing helpers, or manual loops. Python provides this directly in assignment syntax.

How this example works

The list [10, 20, 30, 40, 50] is unpacked into: first = 10 middle = [20, 30, 40] last = 50 This is declarative and avoids error-prone index math.

Why this matters in production

It improves readability for parsing tokens, handling path parts, splitting CLI arguments, and deconstructing structured values. It also communicates intent clearly: one item at start, one at end, everything else in the middle.

Common mistakes

Forgetting that the starred variable becomes a list. Assuming unpacking tolerates mismatched shapes; if required elements are missing, Python raises ValueError. Overusing unpacking in very complex patterns can hurt readability.

Source

• feature_02_extended_unpacking.py

Exact example from code file

def main() -> None:
    first, *middle, last = [10, 20, 30, 40, 50]
    print(first, middle, last)


if __name__ == "__main__":
    main()

Run

uv run src/csharp_to_python_learning/python_only_features/feature_02_extended_unpacking.py

Expected output

• 10 [20, 30, 40] 50