Linter & Formatter & Code Quality Tools¶

Here we'll introduce the linter, formatter and code quality tools used in the project. We won't introduce the tools in detail, but just give a brief introduction and some examples, which are extracted from the official docs.

Ruff and ty (Recommended)¶

• Linter & Formatter: Ruff
• Type Checker: ty

Swiss Army Knife :-)¶

PEP8 -> pycodestyle¶

• PEP 8 – Style Guide for Python Code
• pycodestyle (formerly called pep8) - Python style guide checker

Isort: Style Linter for Import Statements¶

The example from isort doc is very clear:

Before isort:

from my_lib import Object

import os

from my_lib import Object3

from my_lib import Object2

import sys

from third_party import lib15, lib1, lib2, lib3, lib4, lib5, lib6, lib7, lib8, lib9, lib10, lib11, lib12, lib13, lib14

import sys

from __future__ import absolute_import

from third_party import lib3

print("Hey")
print("yo")

After isort:

from __future__ import absolute_import

import os
import sys

from third_party import lib1, lib2, lib3, lib4, lib5, lib6, lib7, lib8, lib9, lib10, lib11, lib12, lib13, lib14, lib15

from my_lib import Object, Object2, Object3

print("Hey")
print("yo")

Flake8: Error & Style Linter, Complexity Analysis¶

For example, we have a file hello.py:

print("Hello, World")

After running flake8 hello.py, we got the following result:

hello.py:1:6: E211 whitespace before '('
hello.py:1:8: E201 whitespace after '('
hello.py:1:23: E202 whitespace before ')'
hello.py:1:25: W292 no newline at end of file

We can see that the flake8 only check the code style, but not fix it. Later, we'll show how to use black to fix the code style automatically.

Black: Code Formatter¶

Use black is simple, just run black . in the project root directory. We can also use black on single file, just run black hello.py.

With the file hello.py:

print("Hello, World")

After running black hello.py, the code style is fixed:

print("Hello, World")

Meantime, black also give us a statistics log:

reformatted hello.py

All done! ✨ 🍰 ✨
1 file reformatted, N files left unchanged.

Ruff: Linter & Formatter¶

As just mentioned before, many people recommend to use Ruff, because it's a very cool tool.

• It's VERY fast.

ty: Type Checker¶

ty is an extremely fast Python type checker written in Rust, from the creators of Ruff.

def greeting(name):
    return "Hello " + name


greeting(123)
greeting(b"Alice")

def greeting(name: str) -> str:
    return "Hello " + name


greeting(3)

prek¶

prek manages repository hooks with a native TOML configuration. This template uses its built-in Rust hooks for file hygiene and local project tools for Ruff and ty, so it does not clone remote hook repositories or create separate hook environments.

[[repos]]
repo = "builtin"
hooks = [
    { id = "check-toml" },
    { id = "check-yaml" },
    { id = "end-of-file-fixer" },
    { id = "trailing-whitespace" },
    { id = "mixed-line-ending", args = ["--fix=lf"] },
]

[[repos]]
repo = "local"
hooks = [
    { id = "ruff-check", name = "ruff check", entry = "uv run ruff check", language = "system", types_or = ["python", "pyi"] },
    { id = "ruff-format", name = "ruff format", entry = "uv run ruff format", language = "system", types_or = ["python", "pyi"] },
    { id = "ty", name = "ty check", entry = "uv run ty check", language = "system", pass_filenames = false, always_run = true },
]

Install the Git hooks and check the whole repository:

uv run prek install
uv run prek run --all-files

SonarLint¶

SonarLint

SQLFluff¶

SQLFluff is a linter for SQL code.