Advanced Iteration: `itertools` and Expression Power

Use the walrus operator `(:=)` to simplify loops that both check and use a value in one pass.

Apply extended unpacking in loop variables (`for a, *rest in rows`) to declaratively destructure data.

Combine, slice, and duplicate iterators efficiently using `itertools.chain`, `islice`, and `tee`.

Perform sequential grouping and cumulative calculations with `itertools.groupby` and `itertools.accumulate`.

Generate combinatorial, windowed, and chunked sequences using `itertools.product`, `itertools.pairwise`, and `itertools.batched`.

Distinguish when to use loops (for side-effects), comprehensions (for collection building), and `itertools` (for streaming pipelines).