Question 1

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 2

What are list/dict/set comprehensions?

Accepted Answer

**Target Audience:** Beginners to intermediate Python developers — you should be comfortable with `for` loops and lists.
**Difficulty:** Easy
**Python version:** Behaviour checked on CPython 3.11, with the scope and bytecode differences also run on 3.12 and 3.13; the examples run in the page on Pyodide 0.25.1 (CPython 3.11.3).

> **How to read this doc:** Every idea is explained in plain language first, then the precise word an interviewer expects is tagged `📌 Interview term:` and defined. The

Question 3

How does Polars LazyFrame query optimization work?

Accepted Answer

**Target Audience:** Developers who have used Polars (or pandas) and want to explain what the lazy API does under the hood.
**Difficulty:** Medium
**Python version:** The two examples are standard-library toy engines that run in the page (Pyodide 0.25.1, CPython 3.11.3) and were checked on CPython 3.11. **Polars itself was not installed in our verification environment**, so Polars snippets here were not run; Polars behaviour is described from the Polars user guide and API reference, cited inline

Question 4

Polars vs pandas: when should you switch in 2025-26?

Accepted Answer

**Target Audience:** Python developers who use pandas and are deciding whether a project should move to Polars, and candidates asked "pandas or Polars?" in a data-engineering interview.
**Difficulty:** Medium
**Python version:** The pandas example ran on CPython 3.13 with **pandas 3.0.5**. The toy model runs in the page (Pyodide 0.25.1, CPython 3.11.3). **Polars was not installed in our verification environment**, so the Polars snippets on this page were not executed: they are shown for the API

Question 5

How does heapq work in Python?

Accepted Answer

**Target Audience:** Developers who have heard "use a heap for a priority queue" and want to know what `heapq` really does, up to candidates expected to explain the algorithm and its costs.
**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). The 3.14 max-heap functions are cited from the docs, not run.

> **How to read this doc:** Each idea is explained in plain language first, then tagged with

Question 6

What are lambda functions and map/filter/reduce?

Accepted Answer

**Target Audience:** Beginners preparing for Python interviews — you know lists, loops and basic functions.
**Difficulty:** Medium
**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** sect

Question 7

What are generators and why use them?

Accepted Answer

**Target Audience:** Python developers who have seen `yield` and want to know what it really does and when it pays off
**Difficulty:** Medium
**Python version:** Checked 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

Question 8

What is the memory difference between a list comprehension and a generator expression?

Accepted Answer

**Target Audience:** Python developers who know both syntaxes and want to be able to quantify and explain the difference
**Difficulty:** Medium
**Python version:** Checked on CPython 3.11 (and in this page on Pyodide 0.25.1, which is CPython 3.11.3); bytecode compared with CPython 3.12. Byte counts are from 64-bit CPython; Pyodide is a 32-bit build, so the examples print comparisons, not raw numbers

> **How to read this doc:** Each idea is explained in plain language first, then tagged with `📌

Question 9

How do you use regular expressions in Python?

Accepted Answer

**Target Audience:** Python developers who copy regexes from the internet and want to understand the `re` module well enough to write, read and debug their own
**Difficulty:** Medium
**Python version:** Checked 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**

Question 10

What is the itertools module used for?

Accepted Answer

**Target Audience:** Python developers who loop a lot and want shorter, faster, lazier loops; candidates who expect "name some itertools functions" in a screen.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11.17 and in the page runner (Pyodide 0.25.1, CPython 3.11.3); the `batched` example was run on CPython 3.13.16 and 3.12.3.

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

PYTHONDECODED.

Easy

What do enumerate and zip do?

What are list/dict/set comprehensions?

Medium

How does Polars LazyFrame query optimization work?

Polars vs pandas: when should you switch in 2025-26?

How does heapq work in Python?

What are lambda functions and map/filter/reduce?

What are generators and why use them?

What is the memory difference between a list comprehension and a generator expression?

How do you use regular expressions in Python?

What is the itertools module used for?

Hard

What is the difference between getattr and getattribute?

What is the descriptor protocol?

PYTHONDECODED.

Easy

What do enumerate and zip do?

What are list/dict/set comprehensions?

Medium

How does Polars LazyFrame query optimization work?

Polars vs pandas: when should you switch in 2025-26?

How does heapq work in Python?

What are lambda functions and map/filter/reduce?

What are generators and why use them?

What is the memory difference between a list comprehension and a generator expression?

How do you use regular expressions in Python?

What is the itertools module used for?

Hard

What is the difference between __getattr__ and __getattribute__?

What is the descriptor protocol?

What is the difference between getattr and getattribute?