What do *args and **kwargs mean? | Interview Question

Q: What do *args and **kwargs mean?

**Target Audience:** Beginners preparing for Python interviews — you know how to write a basic `def` and call it. **Difficulty:** Easy **Python version:** Behaviour checked on CPython 3.11.17 and in the page runner (Pyodide 0.25.1, CPython 3.11.3). > **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. All output shown was produced by actually running the code; the **Verified** section quotes it in full. ## 1. Why This Even Matters — A Story First Imagine a coat check at a theatre. The attendant has one hook with your name on it — that is a normal parameter. But some guests arrive with extra bags. The attendant does not refuse them: unlabelled bags go into one numbered bin, in the order they were handed over, and bags with a name tag go into a labelled cabinet where each tag is the key. `*args` is the numbered bin. `**kwargs` is the labelled cabinet. A function that

The problem

Question presented to candidate: "You see def handler(*args, **kwargs) all over a codebase. What do the single and double star actually do, what types do args and kwargs end up as, and how is that different from putting a star in front of something when you call a function?"

What a strong answer should cover:

In a definition, *args collects any extra positional arguments into a tuple and **kwargs collects any extra keyword arguments into a dict; the names are convention, the stars are the syntax
At a call site the stars do the reverse: f(*seq) spreads an iterable into positional arguments and f(**mapping) spreads a mapping into keyword arguments (string keys only)
Parameter order: regular parameters, then *args, then keyword-only parameters, then **kwargs; anything after *args can only be passed by keyword
The forwarding pattern def wrapper(*args, **kwargs): return func(*args, **kwargs) used by decorators, and the cost: a vaguer signature for callers and type checkers
Details: each call gets a fresh tuple and dict, kwargs keeps the caller order (guaranteed since Python 3.6, PEP 468), and filling the same parameter twice raises TypeError

Code / implementation expected: Optional — a few lines showing packing in a def and unpacking in a call, ideally a small forwarding wrapper.

args
kwargs

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Solution

Target Audience: Beginners preparing for Python interviews — you know how to write a basic def and call it. Difficulty: Easy Python version: Behaviour checked on CPython 3.11.17 and in the page runner (Pyodide 0.25.1, CPython 3.11.3).

How to read this doc: Every idea is explained in plain language first, then tagged with 📌 Interview term: so you also learn the exact words an interviewer expects. All output shown was produced by actually running the code; the Verified section quotes it in full.

1. Why This Even Matters — A Story First

Imagine a coat check at a theatre. The attendant has one hook with your name on it — that is a normal parameter. But some guests arrive with extra bags. The attendant does not refuse them: unlabelled bags go into one numbered bin, in the order they were handed over, and bags with a name tag go into a labelled cabinet where ea

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10 min read · 11 sections

Run the code

Edit the code and run it here. Each console line with an expected value becomes a test.

PythonPacking: what *args and **kwargs receive

Practice

PythonUnpacking at the call site, forwarding and the TypeError gotchas

Practice

Discussion

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