Tutorial#
This tutorial will walk you through the process of integrating Ruff into your project. For a more detailed overview, see Configuration.
Getting Started#
Let's assume that our project structure looks like:
Where numbers.py contains the following code:
from typing import List
import os
def sum_even_numbers(numbers: List[int]) -> int:
"""Given a list of integers, return the sum of all even numbers in the list."""
return sum(num for num in numbers if num % 2 == 0)
To start, we'll install Ruff through PyPI (or with our preferred package manager):
We can then run Ruff over our project via:
❯ ruff check .
numbers/numbers.py:3:8: F401 [*] `os` imported but unused
Found 1 error.
[*] 1 potentially fixable with the --fix option.
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:
Running git diff shows the following:
--- a/numbers/numbers.py
+++ b/numbers/numbers.py
@@ -1,7 +1,5 @@
from typing import List
-import os
-
def sum_even_numbers(numbers: List[int]) -> int:
"""Given a list of integers, return the sum of all even numbers in the list."""
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.
Let's create a pyproject.toml file in our project's root directory:
Running Ruff again, we can see that it now enforces a line length of 79 characters:
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:
[project]
# Support Python 3.10+.
requires-python = ">=3.10"
[tool.ruff]
# Decrease the maximum line length to 79 characters.
line-length = 79
src = ["src"]
Rule Selection#
Ruff supports over 500 lint rules split across over 40 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 enforces the E- and F-prefixed rules, which correspond to those derived from
pycodestyle and Pyflakes, respectively.
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 add the following to our pyproject.toml:
If we run Ruff again, we'll see that it now enforces the pyupgrade rules. In particular, Ruff flags
the use of List instead of its standard-library variant:
❯ ruff check .
numbers/numbers.py:5:31: UP006 [*] Use `list` instead of `List` for type annotations
numbers/numbers.py:6:80: E501 Line too long (83 > 79 characters)
Found 2 errors.
[*] 1 potentially 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:
[tool.ruff]
select = [
"E", # pycodestyle
"F", # pyflakes
"UP", # pyupgrade
"D", # pydocstyle
]
[tool.ruff.pydocstyle]
convention = "google"
If we run Ruff again, we'll see that it now enforces the pydocstyle rules:
❯ ruff check .
numbers/__init__.py:1:1: D104 Missing docstring in public package
numbers/numbers.py:1:1: D100 Missing docstring in public module
numbers/numbers.py:5:31: UP006 [*] Use `list` instead of `List` for type annotations
numbers/numbers.py:5:80: E501 Line too long (83 > 79 characters)
Found 3 errors.
[*] 1 potentially 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 UP006 rule for the List import:
from typing import List
def sum_even_numbers(numbers: List[int]) -> int: # noqa: UP006
"""Given a list of integers, return the sum of all even numbers in the list."""
return sum(num for num in numbers if num % 2 == 0)
Running Ruff again, we'll see that it no longer flags the List import:
❯ ruff check .
numbers/__init__.py:1:1: D104 Missing docstring in public package
numbers/numbers.py:1:1: D100 Missing docstring in public module
numbers/numbers.py:5:80: E501 Line too long (83 > 79 characters)
Found 3 errors.
If we want to ignore a rule for an entire file, we can add a # ruff: noqa comment to the top of
the file:
# ruff: noqa: UP006
from typing import List
def sum_even_numbers(numbers: List[int]) -> int:
"""Given a list of integers, return the sum of all even numbers in the list."""
return sum(num for num in numbers if num % 2 == 0)
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 adds 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 UP006 violations:
Running git diff shows the following:
diff --git a/tutorial/src/main.py b/tutorial/src/main.py
index b9291c5ca..b9f15b8c1 100644
--- a/numbers/numbers.py
+++ b/numbers/numbers.py
@@ -1,6 +1,6 @@
from typing import List
-def sum_even_numbers(numbers: List[int]) -> int:
+def sum_even_numbers(numbers: List[int]) -> int: # noqa: UP006
"""Given a list of integers, return the sum of all even numbers in the list."""
return sum(num for num in numbers if num % 2 == 0)
Continuous Integration#
This tutorial has focused on Ruff's command-line interface, but Ruff can also be used as a pre-commit hook:
- repo: https://github.com/astral-sh/ruff-pre-commit
# Ruff version.
rev: v0.0.270
hooks:
- id: ruff
See Usage for more.
Editor Integrations#
Ruff can also be used as a VS Code extension or alongside any other editor through the Ruff LSP.
See Editor Integrations.