Question 1

What do *args and **kwargs mean?

Accepted Answer

**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**

Question 2

What do the global and nonlocal keywords do?

Accepted Answer

**Target Audience:** Python beginners and intermediate developers preparing for interviews — you should know what a function and a nested function are.
**Difficulty:** Medium
**Python version:** Behaviour and error messages checked on CPython 3.11, 3.12 and 3.13; the examples run in the page on Pyodide 0.25.1 (CPython 3.11.3).

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects.

Question 3

How does functools.lru_cache work?

Accepted Answer

**Target Audience:** Python developers who know basic decorators, up to candidates asked about caching internals
**Difficulty:** Medium
**Python version:** behaviour checked on CPython 3.11 (python3.11 and the in-page Pyodide 0.25.1 runtime)

> **How to read this doc:** Every idea is first explained in plain words. When a term has a precise name an interviewer expects to hear, it is introduced as a 📌 **Interview term** callout. The Quick Glossary at the end lists all of them.

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Question 4

How do default, keyword-only and positional-only parameters work?

Accepted Answer

**Target Audience:** Beginners to intermediate — you can write functions and have seen `*args`.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11.17 and in the page runner (Pyodide 0.25.1, CPython 3.11.3); the `SyntaxError` wording was also checked on 3.12.3 and 3.13.16.

> **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 produc

Question 5

How does Python's name and object reference model work?

Accepted Answer

**Target Audience:** Python beginners and intermediate developers preparing for interviews — you only need to know basic assignment and lists.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11, 3.12 and 3.13; the examples run in the page on Pyodide 0.25.1 (CPython 3.11.3).

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. Every output shown was prod

Question 6

What is Python 3.12's new type parameter syntax (type, generic classes)?

Accepted Answer

**Target Audience:** Python developers who know `TypeVar` and `Generic` and are moving a codebase to Python 3.12 or later.
**Difficulty:** Medium
**Python version:** The syntax needs **Python 3.12+** (defaults need 3.13+). Examples 2 and 3 were run on CPython 3.12.3 and 3.13.16 and are shown as code here, because the page runner is Pyodide 0.25.1 (CPython 3.11.3), where the syntax is a `SyntaxError`. Example 1 runs in the page. Type-checker output is from mypy 2.3.1.

> **How to read this doc:**

Question 7

How do type hints work in Python?

Accepted Answer

**Target Audience:** Python developers who have seen `def f(x: int) -> str:` and want to know what it really does, from the interpreter and from a type checker.
**Difficulty:** Medium
**Python version:** Runtime behaviour checked on CPython 3.11.17 and 3.13, and in the page runner (Pyodide 0.25.1, CPython 3.11.3). Type-checker output is from mypy 2.3.1 (with `--python-version 3.11`) and pyright 1.1.414.

> **How to read this doc:** Every idea is explained in plain language first, then tagged wit

Question 8

What is TypeVarTuple and Unpack for variadic generics?

Accepted Answer

**Target Audience:** Python developers comfortable with `TypeVar` and generics who meet `*Ts` in library stubs, or need to type functions that forward `*args`.
**Difficulty:** Hard
**Python version:** `TypeVarTuple`, `Unpack` and the `*Ts` star syntax are in `typing` from Python 3.11. Runtime behaviour checked on CPython 3.11.17, 3.12.3 and 3.13.16, and in the page runner (Pyodide 0.25.1, CPython 3.11.3). Type-checker output is from mypy 2.3.1 with `--python-version 3.11`.

> **How to read this

Question 9

How do Unpack and TypedDict enable type-safe **kwargs?

Accepted Answer

**Target Audience:** Python developers who know what `**kwargs` is and have written a few type hints, and want to type keyword arguments precisely.
**Difficulty:** Hard
**Python version:** Runtime behaviour checked on CPython 3.11, 3.12 and 3.13; both examples also run in the page on Pyodide 0.25.1 (CPython 3.11.3). Type-checker output is from mypy 2.3.1 and pyright 1.1.414.

> **How to read this doc:** Every idea is explained in plain language first. The exact words an interviewer expects are t

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