Question 1

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 2

How do you read and write files in Python?

Accepted Answer

**Target Audience:** Beginners learning Python, and anyone who wants the precise answer an interviewer expects
**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 pa

Question 3

What is the difference between shallow and deep copy?

Accepted Answer

**Target Audience:** Beginners who have been surprised by "I changed the copy and the original changed too", and anyone preparing for the classic interview follow-ups on `copy`.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11 and 3.13, and in the page runner (Pyodide 0.25.1, CPython 3.11.3). `copy.replace()` needs 3.13.

> **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

Question 4

What is the difference between bytes and str?

Accepted Answer

**Target Audience:** Python developers who handle files, network data or APIs, explained from zero
**Difficulty:** Medium
**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.

## 1.

Question 5

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 6

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 7

How does a for loop work under the hood?

Accepted Answer

**Target Audience:** Python developers who write `for` loops all day and want to know exactly what the interpreter does for one
**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 also compared with 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 block in the **V

Question 8

What is string interning in Python?

Accepted Answer

**Target Audience:** Python developers who know strings, dictionaries and the difference between `==` and `is`. No C knowledge is needed.
**Difficulty:** Medium
**Python version:** Behaviour checked on CPython 3.11 (and repeated on 3.12 and 3.13 where noted). Both examples also run in the page on Pyodide 0.25.1 (CPython 3.11.3).

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

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

PYTHONDECODED.

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