Question 1

How does exception handling work in Python?

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 2

What is a race condition and how do locks prevent it?

Accepted Answer

**Target Audience:** Developers starting with threads who want to understand why shared data goes wrong — no prior concurrency knowledge needed.
**Difficulty:** Medium
**Python version:** Bytecode and behaviour checked on CPython 3.11, 3.12 and 3.13 (standard GIL builds); the in-page example runs 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 exp

Question 3

How does exception propagation work up the call stack?

Accepted Answer

**Target Audience:** Python developers who can write try/except and want to know exactly what happens between a raise and its handler
**Difficulty:** Medium
**Python version:** Checked on CPython 3.11 (and in this page on Pyodide 0.25.1, which is CPython 3.11.3); the thread and process 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. Every output bloc

Question 4

What is asyncio.TaskGroup and why does it replace gather?

Accepted Answer

**Target Audience:** Developers who have written `asyncio` code with `gather` or `create_task` and want to know what TaskGroup changes and when to pick which.
**Difficulty:** Medium
**Python version:** `TaskGroup` needs Python 3.11+. Behaviour checked on CPython 3.11, 3.12 and 3.13 (same output); both examples also 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 `📌 Inte

Question 5

How do you create and chain custom exceptions?

Accepted Answer

**Target Audience:** Python developers who know try/except and want to design errors for a library or service
**Difficulty:** Medium
**Python version:** Checked on CPython 3.11 (and in this page on Pyodide 0.25.1, which is CPython 3.11.3); `add_note` needs 3.11+

> **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

Question 6

How does yield from delegation work?

Accepted Answer

**Target Audience:** Python developers who know what a generator is and want to understand delegation properly; interview candidates who will be asked "isn't it just a loop?".
**Difficulty:** Medium
**Python version:** All behaviour checked on CPython 3.11.17 and in the page runner (Pyodide 0.25.1, CPython 3.11.3); the bytecode comparison was also run on CPython 3.12.3.

> **How to read this doc:** Each idea is explained in plain words first, then tagged with `📌 Interview term:` — that is the e

Question 7

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 8

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 9

How do ThreadPoolExecutor and ProcessPoolExecutor work?

Accepted Answer

**Target Audience:** Developers who have used a loop and a function, and want to run that function many times at once safely — no prior concurrency knowledge needed.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11, 3.12 and 3.13 (standard GIL builds); the in-page example runs 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 intervi

Question 10

How do you use multiple context managers at once?

Accepted Answer

**Target Audience:** Developers who know the single `with` statement and want to combine several resources correctly, including candidates who need the edge cases.
**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. Every out

PYTHONDECODED.

Easy

How does exception handling work in Python?

Medium

What is a race condition and how do locks prevent it?

How does exception propagation work up the call stack?

What is asyncio.TaskGroup and why does it replace gather?

How do you create and chain custom exceptions?

How does yield from delegation work?

How do you raise and split ExceptionGroups manually?

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

How do ThreadPoolExecutor and ProcessPoolExecutor work?

Hard

What is the difference between del, del, and garbage collection?

PYTHONDECODED.

Easy

How does exception handling work in Python?

Medium

What is a race condition and how do locks prevent it?

How does exception propagation work up the call stack?

What is asyncio.TaskGroup and why does it replace gather?

How do you create and chain custom exceptions?

How does yield from delegation work?

How do you raise and split ExceptionGroups manually?

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

How do ThreadPoolExecutor and ProcessPoolExecutor work?

Hard

What is the difference between del, __del__, and garbage collection?

What is the difference between del, del, and garbage collection?