Question 1

How are Python dictionaries implemented and ordered?

Accepted Answer

**Target Audience:** Beginners who use dicts daily and want to know what happens underneath; anyone preparing for a Python interview.
**Difficulty:** Easy
**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).

> **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 in the **Verified** section

Question 2

How does the in operator work in Python?

Accepted Answer

**Target Audience:** Beginners to intermediate Python developers — you should know lists, dicts and sets, and roughly what a class is.
**Difficulty:** Easy
**Python version:** Behaviour, error messages and bytecode checked on CPython 3.11; 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; all of them are repeated in

Question 3

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 4

What is the @property decorator?

Accepted Answer

**Target Audience:** Python beginners who know classes, up to candidates expected to explain descriptors
**Difficulty:** Medium
**Python version:** behaviour checked on CPython 3.11 (python3.11 and the in-page Pyodide 0.25.1 runtime); error messages also checked on 3.12 and 3.13

> **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

Question 5

What useful types does the collections module provide?

Accepted Answer

**Target Audience:** Python learners who know `list` and `dict` and want the tools that make everyday code shorter, up to candidates who need the gotchas and internals.
**Difficulty:** Medium
**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).

> **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. Ever

Question 6

What are abstract base classes and Protocols?

Accepted Answer

**Target Audience:** Developers who know classes and inheritance and have seen `ABC` or `Protocol` in a codebase, up to candidates who need to compare nominal and structural typing precisely.
**Difficulty:** Medium
**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); the differences we saw on 3.12 and 3.13 are called out.

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

Question 7

How does an LRU cache work internally?

Accepted Answer

**Target Audience:** Candidates facing the classic "design an LRU cache" question, and anyone who uses `functools.lru_cache` and wants to know what it does inside.
**Difficulty:** Medium
**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).

> **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 out

Question 8

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 9

How does the bisect module work?

Accepted Answer

**Target Audience:** Beginners who know lists and sorting; candidates who want to write binary search confidently in an interview.
**Difficulty:** Medium
**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). `key=` needs Python 3.10 or newer.

> **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 o

Question 10

What is string interning in Python?

Accepted Answer

**Target Audience:** Python developers who know strings, dictionaries and the difference between `==` and `is`. No C knowledge is needed.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11 (and repeated on 3.12 and 3.13 where noted). Both examples also run in the page on Pyodide 0.25.1 (CPython 3.11.3).

> **How to read this doc:** Every idea is explained in plain words first. When a word appears that an interviewer expects you to know, it is tagged with `📌 Interview t

PYTHONDECODED.

Easy

How are Python dictionaries implemented and ordered?

How does the in operator work in Python?

Medium

What is structural pattern matching (match/case)?

What is the @property decorator?

What useful types does the collections module provide?

What are abstract base classes and Protocols?

How does an LRU cache work internally?

What are bound and unbound methods in Python?

How does the bisect module work?

What is string interning in Python?

Hard

What is the Method Resolution Order (MRO)?

What is the difference between getattr and getattribute?

How does attribute lookup work on a Python object?

PYTHONDECODED.

Easy

How are Python dictionaries implemented and ordered?

How does the in operator work in Python?

Medium

What is structural pattern matching (match/case)?

What is the @property decorator?

What useful types does the collections module provide?

What are abstract base classes and Protocols?

How does an LRU cache work internally?

What are bound and unbound methods in Python?

How does the bisect module work?

What is string interning in Python?

Hard

What is the Method Resolution Order (MRO)?

What is the difference between __getattr__ and __getattribute__?

How does attribute lookup work on a Python object?

What is the difference between getattr and getattribute?