Question 1

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 2

What is the difference between __new__ and __init__?

Accepted Answer

**Target Audience:** Python developers who write classes with `__init__` and have seen `__new__` in library code or an interview question.
**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 by a

Question 3

Why use functools.wraps when writing decorators?

Accepted Answer

**Target Audience:** Developers who can write a basic decorator and want to know why the extra line matters
**Difficulty:** Medium
**Python version:** behaviour checked on CPython 3.11 (python3.11 and the in-page Pyodide 0.25.1 runtime); the 3.12 and 3.13 attribute list was printed on those interpreters

> **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

Question 4

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 5

What is pickling and what are its risks?

Accepted Answer

**Target Audience:** Python developers who know the basics and want to understand serialisation and its security model
**Difficulty:** Medium
**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 o

Question 6

How does multiprocessing share data between processes?

Accepted Answer

**Target Audience:** Python developers who have used threads or `concurrent.futures` and want to know what really happens to their data when work moves to another process.
**Difficulty:** Hard
**Python version:** The pickling example runs in the page on Pyodide 0.25.1 (CPython 3.11.3) and was checked on CPython 3.11. The process examples need real processes, so they were run on CPython 3.12 (and gave identical output on 3.13) on Linux.

> **How to read this doc:** Every idea comes in plain langu

PYTHONDECODED.

Medium

What are common Python security pitfalls?

What is the difference between new and init?

Why use functools.wraps when writing decorators?

How do ThreadPoolExecutor and ProcessPoolExecutor work?

What is pickling and what are its risks?

Hard

How does multiprocessing share data between processes?