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

How do you read TOML with tomllib in Python 3.11+?

Accepted Answer

**Target Audience:** Python developers who configure apps or tools, explained from zero
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11, 3.12 and 3.13 (and in the page's Pyodide 3.11 runtime)

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the exact words an interviewer expects. Every output block in the **Verified** section was copied from a real run of the examples on this page.

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Question 3

How does the logging module work?

Accepted Answer

**Target Audience:** Python developers who use `print` for diagnostics, or who have fought duplicated or missing log lines, and want to understand how `logging` routes a message
**Difficulty:** Medium
**Python version:** Checked on CPython 3.11 (and in this page on Pyodide 0.25.1, which is CPython 3.11.3); 3.12 additions were checked on python3.12

> **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

Question 4

Why does 0.1 + 0.2 != 0.3 in Python, and when do you use Decimal or Fraction?

Accepted Answer

**Target Audience:** Python developers who have been surprised by a float result and want to know exactly why, and which numeric type to use instead
**Difficulty:** Medium
**Python version:** Checked on CPython 3.11 (and in this page on Pyodide 0.25.1, 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 block in the **Verified** section was

Question 5

What are common Python security pitfalls?

Accepted Answer

**Target Audience:** Developers who write Python services or scripts and want a concrete checklist; no security background assumed.
**Difficulty:** Medium
**Python version:** Examples 1 and 2 were run on CPython 3.11 (python3.11 and the in-page Pyodide 0.25.1 runtime, CPython 3.11.3). Example 3 needs `sqlite3` and the `tarfile` filters, which the page runtime does not have, so it was run on python3.12 (and gave identical output on python3.13).

> **How to read this doc:** Each idea is explained

Question 6

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 7

How do TypeAdapter, strict mode, and computed fields work in Pydantic v2?

Accepted Answer

**Target Audience:** Developers who know basic Pydantic `BaseModel` usage and want the v2 features interviewers ask about next.
**Difficulty:** Hard
**Python version:** Pydantic examples run on CPython 3.13 with **pydantic 2.13.5** (pydantic-core 2.46.5). Pydantic is a third-party package, so those examples cannot run in the page; the first example is standard library only and runs in the page (Pyodide 0.25.1, CPython 3.11.3).

> **How to read this doc:** Every idea is explained in plain languag

Question 8

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

Question 9

What is Python 3.12's free-threaded (no-GIL) build and what changes?

Accepted Answer

**Target Audience:** Python developers who know what a thread is and have heard of the GIL, and want accurate version facts and the practical consequences for their code.
**Difficulty:** Hard
**Python version:** Example 1 runs in the page on Pyodide 0.25.1 (CPython 3.11.3) and was also run on CPython 3.11, 3.12 and 3.13. Example 2 was run on the default (GIL) build of CPython 3.13. **We did not have a free-threaded interpreter available**, so statements about how `python3.13t` / `python3.14t` be

PYTHONDECODED.

Easy