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

What is the difference between shallow and deep copy?

Accepted Answer

**Target Audience:** Beginners who have been surprised by "I changed the copy and the original changed too", and anyone preparing for the classic interview follow-ups on `copy`.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11 and 3.13, and in the page runner (Pyodide 0.25.1, CPython 3.11.3). `copy.replace()` needs 3.13.

> **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

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

How does collections.deque work internally?

Accepted Answer

**Target Audience:** Developers who use `deque` as "the fast queue" and want to explain why, up to candidates expected to describe the CPython data structure.
**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 block-growth numbers were identical on python3.13.

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

Question 5

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 6

What is the difference between the call stack and the heap in Python?

Accepted Answer

**Target Audience:** Developers coming from C, C++, Java or Go who want to map "stack vs heap" onto Python, and Python developers debugging recursion or memory
**Difficulty:** Medium
**Python version:** Checked on CPython 3.11, 3.12 and 3.13 (and in this page on Pyodide 0.25.1, which is CPython 3.11.3); all gave identical output

> **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 expect

Question 7

How does a Python list grow in memory?

Accepted Answer

**Target Audience:** Developers who use lists every day and want the memory model an interviewer asks about; no C knowledge needed.
**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 growth rule is a CPython implementation detail and has changed between versions.

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

Question 8

How does a Python set find items?

Accepted Answer

**Target Audience:** Developers who know what a set is and want to explain how membership tests work; no prior hash-table knowledge needed.
**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). Probe constants are CPython implementation details.

> **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 in

Question 9

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 10

What is a weak reference in Python?

Accepted Answer

**Target Audience:** Python developers building caches, event systems or object graphs who need objects to be freed on time
**Difficulty:** Hard
**Python version:** Checked on CPython 3.11, 3.12 and 3.13 (and in this page on Pyodide 0.25.1, which is CPython 3.11.3); all three gave identical output

> **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 **V

PYTHONDECODED.

Easy

How are Python dictionaries implemented and ordered?

Medium

What is the difference between shallow and deep copy?

What are mixins in Python?

How does collections.deque work internally?

What are dataclasses?

What is the difference between the call stack and the heap in Python?

How does a Python list grow in memory?

How does a Python set find items?

What does slots do?

Hard

What is a weak reference in Python?

How does attribute lookup work on a Python object?

What is the descriptor protocol?