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

Why is using a mutable default argument dangerous?

Accepted Answer

**Target Audience:** Beginners to intermediate — you can write functions with default values.
**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 dataclass error message was also checked on 3.12.3.

> **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 actual

Question 3

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 4

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 5

What is a decorator factory (a decorator with arguments)?

Accepted Answer

**Target Audience:** Developers who can write a plain decorator and want configurable ones
**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 This Even Matters — A Story F

Question 6

What is the late-binding closure pitfall in loops?

Accepted Answer

**Target Audience:** Python beginners and intermediate developers preparing for interviews — you should know what a lambda and a list comprehension are.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11, 3.12 and 3.13; the examples run 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, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. Every output show

Question 7

How do closures capture variables in Python?

Accepted Answer

**Target Audience:** Python beginners and intermediate developers preparing for interviews — you should know what a nested function is.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11, 3.12 and 3.13; the examples run 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, then tagged with `📌 Interview term:` so you also learn the exact word an interviewer expects. Every output shown was produced by

Question 8

How does the asyncio event loop schedule coroutines?

Accepted Answer

**Target Audience:** Developers comfortable with `async`/`await` who want to explain, precisely, how asyncio orders and resumes work.
**Difficulty:** Hard
**Python version:** Example 1 (a model scheduler, no asyncio) runs in the page on Pyodide 0.25.1 (CPython 3.11.3) and was checked on CPython 3.11. Example 2 uses the real asyncio loop and `asyncio.eager_task_factory`, so it was run on CPython 3.12 (3.13 printed the same). Source references are to CPython 3.12 `Lib/asyncio/base_events.py` and `

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Easy