Tutorial
This tutorial will walk you through the process of integrating Ruff's linter and formatter into your project. For a more detailed overview, see Configuring Ruff.
Getting Started
To start, we'll initialize a project using uv:
This command creates a Python project with the following structure:
We'll then clear out the auto-generated content in src/numbers/__init__.py
and create src/numbers/calculate.py with the following code:
from typing import Iterable
import os
def sum_even_numbers(numbers: Iterable[int]) -> int:
"""Given an iterable of integers, return the sum of all even numbers in the iterable."""
return sum(
num for num in numbers
if num % 2 == 0
)
Next, we'll add Ruff to our project:
We can then run the Ruff linter over our project via uv run ruff check:
$ uv run ruff check
src/numbers/calculate.py:3:8: F401 [*] `os` imported but unused
Found 1 error.
[*] 1 fixable with the `--fix` option.
Note
As an alternative to uv run, you can also run Ruff by activating the project's virtual
environment (source .venv/bin/active on Linux and macOS, or .venv\Scripts\activate on
Windows) and running ruff check directly.
Ruff identified an unused import, which is a common error in Python code. Ruff considers this a
"fixable" error, so we can resolve the issue automatically by running ruff check --fix:
Running git diff shows the following:
--- a/src/numbers/calculate.py
+++ b/src/numbers/calculate.py
@@ -1,7 +1,5 @@
from typing import Iterable
-import os
-
def sum_even_numbers(numbers: Iterable[int]) -> int:
"""Given an iterable of integers, return the sum of all even numbers in the iterable."""
return sum(
num for num in numbers
if num % 2 == 0
)
Note Ruff runs in the current directory by default, but you can pass specific paths to check:
Now that our project is passing ruff check, we can run the Ruff formatter via ruff format:
Running git diff shows that the sum call was reformatted to fit within the default 88-character
line length limit:
--- a/src/numbers/calculate.py
+++ b/src/numbers/calculate.py
@@ -3,7 +3,4 @@ from typing import Iterable
def sum_even_numbers(numbers: Iterable[int]) -> int:
"""Given an iterable of integers, return the sum of all even numbers in the iterable."""
- return sum(
- num for num in numbers
- if num % 2 == 0
- )
+ return sum(num for num in numbers if num % 2 == 0)
Thus far, we've been using Ruff's default configuration. Let's take a look at how we can customize Ruff's behavior.
Configuration
To determine the appropriate settings for each Python file, Ruff looks for the first
pyproject.toml, ruff.toml, or .ruff.toml file in the file's directory or any parent directory.
To configure Ruff, we'll add the following to the configuration file in our project's root directory:
[tool.ruff]
# Set the maximum line length to 79.
line-length = 79
[tool.ruff.lint]
# Add the `line-too-long` rule to the enforced rule set. By default, Ruff omits rules that
# overlap with the use of a formatter, like Black, but we can override this behavior by
# explicitly adding the rule.
extend-select = ["E501"]
Running Ruff again, we see that it now enforces a maximum line width, with a limit of 79:
For a full enumeration of the supported settings, see Settings. For our project specifically, we'll want to make note of the minimum supported Python version:
Rule Selection
Ruff supports over 800 lint rules split across over 50 built-in plugins, but determining the right set of rules will depend on your project's needs: some rules may be too strict, some are framework-specific, and so on.
By default, Ruff enables Flake8's F rules, along with a subset of the E rules, omitting any
stylistic rules that overlap with the use of a formatter, like ruff format or
Black.
If you're introducing a linter for the first time, the default rule set is a great place to start: it's narrow and focused while catching a wide variety of common errors (like unused imports) with zero configuration.
If you're migrating to Ruff from another linter, you can enable rules that are equivalent to those enforced in your previous configuration. For example, if we want to enforce the pyupgrade rules, we can set our configuration file to the following:
If we run Ruff again, we'll see that it now enforces the pyupgrade rules. In particular, Ruff flags
the use of the deprecated typing.Iterable instead of collections.abc.Iterable:
$ uv run ruff check
src/numbers/calculate.py:1:1: UP035 [*] Import from `collections.abc` instead: `Iterable`
Found 1 error.
[*] 1 fixable with the `--fix` option.
Over time, we may choose to enforce additional rules. For example, we may want to enforce that all functions have docstrings:
If we run Ruff again, we'll see that it now enforces the pydocstyle rules:
$ uv run ruff check
src/numbers/__init__.py:1:1: D104 Missing docstring in public package
src/numbers/calculate.py:1:1: UP035 [*] Import from `collections.abc` instead: `Iterable`
|
1 | from typing import Iterable
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^ UP035
|
= help: Import from `collections.abc`
src/numbers/calculate.py:1:1: D100 Missing docstring in public module
Found 3 errors.
[*] 1 fixable with the `--fix` option.
Ignoring Errors
Any lint rule can be ignored by adding a # noqa comment to the line in question. For example,
let's ignore the UP035 rule for the Iterable import:
from typing import Iterable # noqa: UP035
def sum_even_numbers(numbers: Iterable[int]) -> int:
"""Given an iterable of integers, return the sum of all even numbers in the iterable."""
return sum(num for num in numbers if num % 2 == 0)
Running ruff check again, we'll see that it no longer flags the Iterable import:
$ uv run ruff check
src/numbers/__init__.py:1:1: D104 Missing docstring in public package
src/numbers/calculate.py:1:1: D100 Missing docstring in public module
Found 2 errors.
If we want to ignore a rule for an entire file, we can add the line # ruff: noqa: {code} anywhere
in the file, preferably towards the top, like so:
# ruff: noqa: UP035
from typing import Iterable
def sum_even_numbers(numbers: Iterable[int]) -> int:
"""Given an iterable of integers, return the sum of all even numbers in the iterable."""
return sum(num for num in numbers if num % 2 == 0)
For more in-depth instructions on ignoring errors, please see Error suppression.
Adding Rules
When enabling a new rule on an existing codebase, you may want to ignore all existing violations of that rule and instead focus on enforcing it going forward.
Ruff enables this workflow via the --add-noqa flag, which will add a # noqa directive to each
line based on its existing violations. We can combine --add-noqa with the --select command-line
flag to add # noqa directives to all existing UP035 violations:
Running git diff shows the following:
diff --git a/numbers/src/numbers/calculate.py b/numbers/src/numbers/calculate.py
index 71fca60c8d..e92d839f1b 100644
--- a/numbers/src/numbers/calculate.py
+++ b/numbers/src/numbers/calculate.py
@@ -1,4 +1,4 @@
-from typing import Iterable
+from typing import Iterable # noqa: UP035
Integrations
This tutorial has focused on Ruff's command-line interface, but Ruff can also be used as a
pre-commit hook via ruff-pre-commit:
- repo: https://github.com/astral-sh/ruff-pre-commit
# Ruff version.
rev: v0.11.6
hooks:
# Run the linter.
- id: ruff
# Run the formatter.
- id: ruff-format
Ruff can also be integrated into your editor of choice. Refer to the Editors section for more information.
For other integrations, see the Integrations section.