Q: How does comparison chaining (a < b < c) work?

**Target Audience:** Beginners who have seen `0 **How to read this doc:** Plain words first, then a `📌 Interview term:` callout with the exact term. All outputs are from real runs; the **Verified** section quotes them in full. ## 1. Why This Eve

Question 1

How does comparison chaining (a < b < c) work?

Accepted Answer

**Target Audience:** Beginners who have seen `0 <= x < 10` and want to know exactly what it means; candidates who want the CPython detail.
**Difficulty:** Easy
**Python version:** Checked on CPython 3.11.17 and in the page runner (Pyodide 0.25.1, CPython 3.11.3); bytecode also shown from 3.13.16.

> **How to read this doc:** Plain words first, then a `📌 Interview term:` callout with the exact term. All outputs are from real runs; the **Verified** section quotes them in full.

## 1. Why This Eve

Question 2

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 3

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 4

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

Question 5

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 6

What is the difference between the call stack and the heap in Python?

Accepted Answer

**Target Audience:** Developers coming from C, C++, Java or Go who want to map "stack vs heap" onto Python, and Python developers debugging recursion or memory
**Difficulty:** Medium
**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); all gave identical output

> **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 expect

Question 7

How does Timsort make Python's sort fast and stable?

Accepted Answer

**Target Audience:** Developers who know what sorting is and have heard of merge sort and insertion sort. Everything else is explained.
**Difficulty:** Medium
**Python version:** Behaviour and comparison counts checked on CPython 3.11 and 3.12 (identical counts). Both examples also run in the page on Pyodide 0.25.1 (CPython 3.11.3).

> **How to read this doc:** Each idea is explained in plain words first. When a word appears that an interviewer expects you to know, it is tagged with `📌 Intervie

Question 8

What are generics and TypeVar in Python?

Accepted Answer

**Target Audience:** Python developers who use type hints and want to write functions and classes that work for many types without falling back to `Any`.
**Difficulty:** Medium
**Python version:** 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`. This page uses the `TypeVar` spelling that works on every supported version; the 3.12 shorthand is covered in [Python 3.12 type para

Question 9

What is a context manager?

Accepted Answer

**Target Audience:** Python learners who use `with open(...)` without knowing what it does, up to candidates who need the exact protocol and CPython details.
**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); spot checks on 3.12 and 3.13 are noted where made.

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌 Interview term:` so you also learn the

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

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