# Given seen_users = frozenset({'ada', 'linus', 'grace'}), try to add a user (this would fail on a mut

Canonical URL: <https://datadriven.io/problems/given-seenusers-frozensetada-linus-grace-try-b8f2f2e8>

Domain: Python · Difficulty: medium

## Problem

Given seen_users = frozenset({'ada', 'linus', 'grace'}), try to add a user (this would fail on a mutable set). Instead, build a new frozenset by unioning with {'margaret'}. Print the sorted list of the new frozenset.

## Related

- [All practice problems](https://datadriven.io/problems)
- [Mock interview mode](https://datadriven.io/interview/given-seenusers-frozensetada-linus-grace-try-b8f2f2e8)
- [Python Interview Questions](https://datadriven.io/python-interview-questions)
- [Data Engineering Interview Prep Guide](https://datadriven.io/data-engineer-interview-prep)
- [Daily Challenge](https://datadriven.io/daily)

---

Source: DataDriven (https://datadriven.io). 100% free data engineering interview prep. Live code execution against Postgres 16, Python 3.11, and Spark sandboxes. No paywall, no premium tier, no signup gate.