Lab Information
The xFusionCorp Industries ML team enforces code quality with ruff and black on every pull request. The project at /root/code/fraud-detection/ currently fails both tools. Make it pass them.
The project at /root/code/fraud-detection/ contains a pyproject.toml and sample sources under src/.
The corrected project must meet the following requirements:
ruff and black are both configured with a line length of 120.
ruff lint rule selection includes E, F, W, and I, and is declared under [tool.ruff.lint] – The schema required by ruff 0.1 and later.
Running ruff check src/ from the project directory exits with status 0.
Running black --check src/ from the project directory exits with status 0.
Review the existing configuration and source files, and correct everything that prevents the two commands above from exiting cleanly.
ruff, black, and mypy are already installed.
Lab Solutions
🧭 Part 1: Lab Step-by-Step Guidelines
Step 1 — Move into the project directory
cd /root/code/fraud-detection
Step 2 — Inspect the current configuration
Check the existing pyproject.toml:
cat pyproject.toml
Look for:
incorrect Ruff schema
wrong line length
missing lint selections
Step 3 — Fix pyproject.toml
Open the file:
vi pyproject.toml
Replace or correct the contents to include:
[project]
name = "fraud-detection"
version = "0.1.0"
[tool.black]
line-length = 120
[tool.ruff]
line-length = 120
[tool.ruff.lint]
select = ["E", "F", "W", "I"]
Step 4 — Run Ruff Check
Run:
ruff check src/
If errors appear, fix them.
Example issues:
root@controlplane ~/code/fraud-detection via 🐍 v3.12.3 ➜ ruff check src/
I001 [*] Import block is un-sorted or un-formatted
--> src/data/process_data.py:1:1
|
1 | / import os
2 | | import pandas as pd
| |___________________^
|
help: Organize imports
F401 [*] `os` imported but unused
--> src/data/process_data.py:1:8
|
1 | import os
| ^^
2 | import pandas as pd
|
help: Remove unused import: `os`
Found 2 errors.
[*] 2 fixable with the `--fix` option.
Step 5 — Auto-fix Ruff Issues (Recommended)
Run:
ruff check src/ --fix
ruff check src/
Example Output:
root@controlplane ~/code/fraud-detection via 🐍 v3.12.3 ➜ ruff check src/ --fix
Found 1 error (1 fixed, 0 remaining).
root@controlplane ~/code/fraud-detection via 🐍 v3.12.3 ➜ ruff check src/
All checks passed!
Step 6 — Format with Black
Run:
black src/
Expected Output:
black src/
All done! ✨ 🍰 ✨
5 files left unchanged.
Step 8 — Final Ruff Validation
Run again:
ruff check src/
Expected:
root@controlplane ~/code/fraud-detection via 🐍 v3.12.3 ➜ black --check src/
All done! ✨ 🍰 ✨
5 files would be left unchanged.
🧠 Part 2: Simple Beginner-Friendly Explanation
What is this lab about?
This lab focuses on Python code quality and formatting.
The project must pass:
Ruff → linting tool
Black → formatting tool
These tools help teams maintain:
clean code
consistent style
fewer bugs
What is Ruff?
Ruff is a fast Python linter.
It checks for problems like:
unused imports
syntax issues
bad formatting
import ordering problems
Example:
import os
If os is never used:
Ruff reports an error.
What is Black?
Black is an automatic Python formatter.
It rewrites code into a consistent style.
Example:
Before:
x=[1,2,3]
After Black:
x = [1, 2, 3]
Why Line Length Matters
The lab requires:
line-length = 120
This means:
code lines may be up to 120 characters long
both Ruff and Black must use the same limit
If tools use different limits:
formatting conflicts happen
Understanding Ruff Rule Selection
The lab requires:
[tool.ruff.lint]
select = ["E", "F", "W", "I"]
These rule groups mean:
Rule Purpose
E pycodestyle errors
F Pyflakes checks
W style warnings
I import sorting
Why [tool.ruff.lint] Is Important
Older Ruff versions allowed:
[tool.ruff]
select = [...]
But Ruff 0.1+ requires:
[tool.ruff.lint]
Using the old schema causes configuration errors.
Why Run ruff check src/ --fix
This command:
automatically fixes many problems
sorts imports
removes simple issues
It saves time compared to manual editing.
Why Run black src/
This command reformats all Python files under:
src/
After formatting, this check should pass:
black --check src/