zip()

                zip(*iterables, strict=False)
              

Purpose

zip(*iterables) walks two or more iterables together, producing tuples that pair up the item at each shared position — the standard way to loop over parallel data (names and their scores, labels and values) without indexing into each list separately.

Example

names = ["apples", "bananas", "cherries"]
quantities = [12, 3, 40]

for name, qty in zip(names, quantities):
    print(f"{name}: {qty}")

apples: 12
bananas: 3
cherries: 40

Behavior notes

• zip stops as soon as its shortest input iterable is exhausted — if names had four items and quantities had three, the fourth name is silently dropped, with no error.
• Since Python 3.10, passing strict=True makes zip raise a ValueError instead of silently truncating when the iterables have different lengths — worth reaching for whenever mismatched lengths would actually be a bug rather than something expected.
• zip is lazy, like enumerate — it produces tuples one at a time rather than building a list of them up front. Wrap it in list(...) to see all the pairs at once.
• zip(*pairs) (with a single already-zipped argument, unpacked) reverses a zip — a common, if slightly dense-looking, idiom for “transposing” paired data back into separate sequences.

Common mistakes

• Assuming a length mismatch between the inputs raises an error by default — it doesn’t; the extra items in the longer iterable are silently discarded unless strict=True is passed.
• Indexing into two lists in a loop (for i in range(len(names)): names[i], quantities[i]) instead of zipping them — it works, but it’s more code and more opportunities for an off-by-one mistake.

Implementation notes

zip’s pairing and shortest-wins truncation are language guarantees. strict=True is a real, version-gated addition — unavailable before Python 3.10.