---
type: challenge
title: "The Methods"
xp: 50
duration: 30
difficulty: 2
---

# The Methods

> **[INCOMING — Mission Control, Earth]**
>
> Cadet, every string carries a toolkit of methods. The most-used:
>
> - `s.upper()` — uppercase copy
> - `s.lower()` — lowercase copy
> - `s.strip()` — drops leading/trailing whitespace
> - `s.replace(a, b)` — every `a` becomes `b`
>
> Methods can be *chained* — each returns a new string you can call
> the next on:
>
> ```python
> "  Hello World  ".strip().lower().replace(" ", "_")
> # → "hello_world"
> ```
>
> Implement `transform(s)` that returns a dict with three keys:
>
> - `upper` — input uppercased
> - `lower` — input lowercased
> - `clean` — input stripped, lowercased, spaces replaced by `_`
>
> [END TRANSMISSION]

## Your Task

In `starter/starter.py`, build the dict using the four methods.

## Objectives

- `transform("  Hello World  ")["clean"]` returns `"hello_world"`
- All three keys present and correct for any string