Question 1

How do you convert between Python objects and JSON?

Accepted Answer

**Target Audience:** Beginners learning Python, and developers who want the edge cases an interviewer probes
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11 (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

Question 2

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 3

What is the @property decorator?

Accepted Answer

**Target Audience:** Python beginners who know classes, up to candidates expected to explain descriptors
**Difficulty:** Medium
**Python version:** behaviour checked on CPython 3.11 (python3.11 and the in-page Pyodide 0.25.1 runtime); error messages also checked on 3.12 and 3.13

> **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

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

How do you raise and split ExceptionGroups manually?

Accepted Answer

**Target Audience:** Python developers who have seen `ExceptionGroup` come out of a `TaskGroup` and want to create, inspect and split groups themselves.
**Difficulty:** Medium
**Python version:** Python 3.11+ (PEP 654). Behaviour checked on CPython 3.11, 3.12 and 3.13 (identical output); both examples run in this page on Pyodide 0.25.1 (CPython 3.11.3).

> **How to read this doc:** Every idea comes in plain language first. Words an interviewer expects you to use are tagged `📌 Interview term:` a

Question 6

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 7

What is a metaclass?

Accepted Answer

**Target Audience:** Python developers who are comfortable with classes and want to know what sits one level above them
**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); the hook order is identical on all of them

> **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

Question 8

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 9

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 10

How do Unpack and TypedDict enable type-safe **kwargs?

Accepted Answer

**Target Audience:** Python developers who know what `**kwargs` is and have written a few type hints, and want to type keyword arguments precisely.
**Difficulty:** Hard
**Python version:** Runtime behaviour checked on CPython 3.11, 3.12 and 3.13; both examples also run in the page on Pyodide 0.25.1 (CPython 3.11.3). Type-checker output is from mypy 2.3.1 and pyright 1.1.414.

> **How to read this doc:** Every idea is explained in plain language first. The exact words an interviewer expects are t

PYTHONDECODED.

Easy