Question 1

How do you work with dictionaries (get, setdefault, items, merging)?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — no prior knowledge assumed beyond variables and lists.
**Difficulty:** Easy
**Python version:** Checked on CPython 3.11 and the page runner (Pyodide 0.25.1 = CPython 3.11.3). The `|` and `|=` operators need Python 3.9 or newer.

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` — the precise word an interviewer expects you to use. Every output shown was produced by act

Question 2

What is the difference between append, extend and insert on a list?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — you need to know what a list is; nothing more.
**Difficulty:** Easy
**Python version:** Checked on CPython 3.11 (64-bit Linux) and the page runner (Pyodide 0.25.1 = CPython 3.11.3, a 32-bit WebAssembly build).

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` — the precise word an interviewer expects you to use. Every output shown was produced by actually running the

Question 3

What set operations does Python support?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — you need to know what a list is; school-level Venn diagrams help.
**Difficulty:** Easy
**Python version:** Checked on CPython 3.11 and the page runner (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:` — the precise word an interviewer expects you to use. Every output shown was produced by actually running the code on CPython 3.11 and

Question 4

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 5

What is the difference between an iterable and an iterator?

Accepted Answer

**Target Audience:** Python developers who loop over things every day and want the precise model behind it
**Difficulty:** Medium
**Python version:** Checked on CPython 3.11 (and in this page on Pyodide 0.25.1, which is CPython 3.11.3); the protocol is the same on 3.12 and 3.13

> **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 wa

Question 6

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 7

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 8

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 9

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 10

How does functools.reduce fold a sequence?

Accepted Answer

**Target Audience:** Developers meeting `reduce` for the first time, or coming from JavaScript `Array.prototype.reduce` or functional languages; candidates expected to trace a fold by hand.
**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 keyword-argument check was also run on 3.12.3 and 3.13.16.

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

PYTHONDECODED.

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