Question 1

How does iterable unpacking work?

Accepted Answer

**Target Audience:** Beginners to intermediate Python developers — you should know what a list and a tuple are.
**Difficulty:** Easy
**Python version:** Behaviour and `dis` output checked on CPython 3.11 (3.12 where noted); the examples also run in the page on Pyodide 0.25.1 (CPython 3.11.3).

> **How to read this doc:** Ideas come in plain language first. Words an interviewer expects you to use are tagged `📌 Interview term:` and defined on the spot, then listed again in the Quick Glossary. All

Question 2

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 3

What are mixins in Python?

Accepted Answer

**Target Audience:** Developers who know single inheritance and want to use (and explain) multiple inheritance the way Python libraries do.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11.17, 3.12 and 3.13, 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

Question 4

What is structural pattern matching (match/case)?

Accepted Answer

**Target Audience:** Python developers who know `if`/`elif`, lists, dicts and classes and have never used `match`, plus anyone who wants the exact rules an interviewer probes.
**Difficulty:** Medium
**Python version:** `match` needs Python 3.10+. Behaviour and bytecode checked on CPython 3.11 (gotchas re-run on 3.13); both examples also run in the page on Pyodide 0.25.1 (CPython 3.11.3).

> **How to read this doc:** Ideas come in plain language first. The words an interviewer expects you to use

Question 5

What are decorators in Python?

Accepted Answer

**Target Audience:** Python beginners who have written functions, up to candidates preparing for mid-level interviews
**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.

## 1. Why Th

Question 6

How do you create and chain custom exceptions?

Accepted Answer

**Target Audience:** Python developers who know try/except and want to design errors for a library or service
**Difficulty:** Medium
**Python version:** Checked on CPython 3.11 (and in this page on Pyodide 0.25.1, which is CPython 3.11.3); `add_note` needs 3.11+

> **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 block in the **Verified** section was copied from a

Question 7

What are bound and unbound methods in Python?

Accepted Answer

**Target Audience:** Developers who can write a class and want to understand what `self` really is — beginners welcome, intermediate developers will find the CPython detail.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11 and 3.13 (identical output; bytecode shown for 3.11 and 3.12); every example also runs 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. When a word appears that an interview

Question 8

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 9

How do you enforce match/case exhaustiveness in Python?

Accepted Answer

**Target Audience:** Python developers who use `match` or `if`/`elif` chains over enums or tagged types and want missing cases caught automatically.
**Difficulty:** Medium
**Python version:** `assert_never` needs Python 3.11+ (or `typing_extensions`). Runtime behaviour checked on CPython 3.11; both examples also run in the page on Pyodide 0.25.1 (CPython 3.11.3). Checker output is from mypy 2.3.1 and pyright 1.1.414.

> **How to read this doc:** Ideas come in plain language first. Terms an inter

Question 10

What is the Method Resolution Order (MRO)?

Accepted Answer

**Target Audience:** Python developers who have used inheritance but never had to think about the order of lookup, up to candidates who need to explain C3 and `super()` precisely.
**Difficulty:** Hard
**Python version:** Behaviour checked on CPython 3.11 (python3.11 and the in-page Pyodide 0.25.1 runtime, which is CPython 3.11.3), with the MRO error message also checked on 3.13.

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so

PYTHONDECODED.

Easy

How does iterable unpacking work?

What do *args and **kwargs mean?

Medium

What are mixins in Python?

What is structural pattern matching (match/case)?

What are decorators in Python?

How do you create and chain custom exceptions?

What are bound and unbound methods in Python?

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

How do you enforce match/case exhaustiveness in Python?

Hard

What is the Method Resolution Order (MRO)?

What is TypeVarTuple and Unpack for variadic generics?

What is __init_subclass__ in Python?

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