Ruff: linting and import sorting
Overview
**Memorizable line:** Ruff is an extremely fast tool that finds mistakes in your code and sorts your imports. While Black fixes spaces, Ruff fixes logic mistakes and bad practices. This is called `linting`. Here is code with mistakes: ```python import os import sys def calculate(): x = 10 return 5 ``` Ruff will yell at you because `os` and `sys` are imported but never used. It will also warn you that the variable `x` is created but never used. Ruff also sorts your imports alphabetically and groups them cleanly. You run it from your terminal: `ruff check my_file.py`. **Analogy:** If Black is the person who irons your shirt, Ruff is the person who tells you your shirt is inside-out and missing a button.
It catches bugs before you even run your code. It is written in Rust, making it hundreds of times faster than older tools.
Where used: FastAPI, Django
Why learn this
- Helps you find unused variables and imports instantly.
Code walkthrough
def run():
unused_var = 42
return 'Success'
print(run())Focus: unused_var = 42
Aha moment
import math
def calc(): return 5
print(calc())Prediction: Will this code crash when we run it in Python?
Common guess: Yes, because math is not used.
Python will run it perfectly. Ruff is the tool that complains about unused imports, not Python.
Common mistakes
- Ignoring warnings: If Ruff gives a warning, fix it. Do not leave unused imports in your file.
Recall questions
- Explain Ruff in your own words, as if to a classmate.
- What is the difference between Ruff and Black?
Understanding checks
Which tool would complain that you wrote `import math` but never used it? A: Black, or B: Ruff?
B
Ruff is a linter that finds unused imports. Black only formats spacing.
What mistake would Ruff find in this code?
The variable `total` is assigned but never used.
Linters check for variables that are created but ignored, as it often means a bug.
Practice tasks
Fix a linting error
Given this code, fix the issue that Ruff would complain about by removing the unused variable.
Challenge
Write clean code
Write a function `say_hi()` that returns 'hi'. Do not import anything. Do not create any unused variables.
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