Question 1

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 2

What is composition versus inheritance?

Accepted Answer

**Target Audience:** Developers who can write classes and subclasses and want to know how to choose between the two main ways of reusing code.
**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

Question 3

What are dataclasses?

Accepted Answer

**Target Audience:** Python developers who write classes by hand and want to know what `@dataclass` generates, which options matter, and where its limits are.
**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). `slots`, `kw_only` and `KW_ONLY` need 3.10+.

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

Question 4

What does __slots__ do?

Accepted Answer

**Target Audience:** Python developers who know classes and instance attributes and want to understand what `__slots__` changes under the hood.
**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). Memory figures are from our CPython runs and vary by version.

> **How to read this doc:** Every idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exa

Question 5

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

Question 6

What is __init_subclass__ in Python?

Accepted Answer

**Target Audience:** Intermediate Python developers comfortable with classes and inheritance who have heard of metaclasses and want the simpler tool.
**Difficulty:** Hard
**Python version:** Behaviour checked on CPython 3.11 (outputs identical on 3.12 and 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. Terms an interviewer expects you to use are tagged `📌 Interview term:` and defined where they appear

PYTHONDECODED.

Medium

What are mixins in Python?

What is composition versus inheritance?

What are dataclasses?

What does slots do?

Hard

What is the Method Resolution Order (MRO)?

What is __init_subclass__ in Python?