Question 1

What is the enum module and when should you use it?

Accepted Answer

**Target Audience:** Python beginners and intermediate developers who use strings or numbers as status codes and want to know what `enum` adds
**Difficulty:** Easy
**Python version:** Checked on CPython 3.11 (and in this page on Pyodide 0.25.1, which is CPython 3.11.3); differences in 3.12 are called out where we ran 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. Ever

Question 2

What is the difference between a module and a package?

Accepted Answer

**Target Audience:** Beginners learning Python, and anyone preparing for a Python interview
**Difficulty:** Easy
**Python version:** Every example was run 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 copied from a real run of the examples on th

Question 3

What do *args and **kwargs mean?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — you know how to write a basic `def` and call it.
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11.17 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 actually running the code; the **Verified**

Question 4

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 5

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 6

What do enumerate and zip do?

Accepted Answer

**Target Audience:** Beginners to intermediate Python developers preparing for interviews — you only need to know what a list and a `for` loop are.
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11 (and 3.12 where noted); every example also runs 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. When a word appears that an interviewer expects you to know, it is tagged with `📌 Interview term:` and

Question 7

What are dunder (magic) methods?

Accepted Answer

**Target Audience:** Beginners who know how to write a basic `class`, up to intermediate developers preparing for Python interviews.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11 and 3.13 (identical output); every example also runs 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. When a word appears that an interviewer expects you to know, it is tagged with `📌 Interview term:` and defined

Question 8

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 9

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 10

What are decorators in Python?

Accepted Answer

**Target Audience:** Python beginners who have written functions, up to candidates preparing for mid-level interviews
**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 Th

PYTHONDECODED.

Easy

What is the enum module and when should you use it?

What is the difference between a module and a package?

What do *args and **kwargs mean?

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

How do you convert between Python objects and JSON?

What do enumerate and zip do?

Medium

What are dunder (magic) methods?

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

What is composition versus inheritance?

What are decorators in Python?

How do generator pipelines stream data lazily?

What is the difference between new and init?

What are lambda functions and map/filter/reduce?

What are dataclasses?

Hard

How does the Python import system work?

What is a metaclass?

What is the Method Resolution Order (MRO)?

What is __init_subclass__ in Python?

PYTHONDECODED.

Easy

What is the enum module and when should you use it?

What is the difference between a module and a package?

What do *args and **kwargs mean?

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

How do you convert between Python objects and JSON?

What do enumerate and zip do?

Medium

What are dunder (magic) methods?

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

What is composition versus inheritance?

What are decorators in Python?

How do generator pipelines stream data lazily?

What is the difference between __new__ and __init__?

What are lambda functions and map/filter/reduce?

What are dataclasses?

Hard

How does the Python import system work?

What is a metaclass?

What is the Method Resolution Order (MRO)?

What is __init_subclass__ in Python?

What is the difference between new and init?