Question 1

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 2

What is uv and why is it replacing pip/poetry in 2025-26?

Accepted Answer

**Target Audience:** Python developers who know pip and venv and keep hearing about uv, and candidates asked about modern Python tooling
**Difficulty:** Easy
**Python version:** The in-page examples were run on CPython 3.11 and in this page (Pyodide 0.25.1, CPython 3.11.3). The shell sessions were run with uv 0.11.32 on Linux against python3.11; uv changes quickly, so check `uv --version` and the docs for your release.

> **How to read this doc:** Each idea is explained in plain language first,

Question 3

How does Pydantic v2 validation work (BaseModel, field_validator, mode)?

Accepted Answer

**Target Audience:** Python developers who have seen Pydantic models in FastAPI or config code and want to know exactly what runs, in which order, when data is validated.
**Difficulty:** Medium
**Python version:** Pydantic examples verified with pydantic 2.13.5 (pydantic-core 2.46.5) on CPython 3.13. Pydantic is a third-party package, so those two examples are shown as code for the playground; the first example is a standard-library model of the pipeline that runs in the page on Pyodide 0.25.1 (

Question 4

What is except* and ExceptionGroup in Python 3.11+?

Accepted Answer

**Target Audience:** Python developers who know try/except and are meeting exception groups for the first time
**Difficulty:** Medium
**Python version:** `ExceptionGroup` and `except*` need Python 3.11+; checked on CPython 3.11 (and in this page on Pyodide 0.25.1, which is CPython 3.11.3), the asyncio example on CPython 3.12

> **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 interviewer expects. E

Question 5

What does typing.Self do and why does it beat TypeVar for methods?

Accepted Answer

**Target Audience:** Python developers who write class hierarchies with chainable methods or alternative constructors and use a type checker.
**Difficulty:** Medium
**Python version:** `typing.Self` exists from Python 3.11. Runtime behaviour checked on CPython 3.11.17 and in the page runner (Pyodide 0.25.1, CPython 3.11.3). Type-checker output is from mypy 2.3.1 with `--python-version 3.11`.

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

PYTHONDECODED.

Easy

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

What is uv and why is it replacing pip/poetry in 2025-26?

Medium

How does Pydantic v2 validation work (BaseModel, field_validator, mode)?

What is except* and ExceptionGroup in Python 3.11+?

What does typing.Self do and why does it beat TypeVar for methods?