ruff 0.0.42

An extremely fast Python linter, written in Rust.

ruff

An extremely fast Python linter, written in Rust.

Linting the CPython codebase from scratch.

• ⚡️ 10-100x faster than existing linters
• 🐍 Installable via pip
• 🤝 Python 3.10 compatibility
• 🛠️ pyproject.toml support
• 📦 ESLint-inspired cache support
• 🔧 ESLint-inspired --fix support
• 👀 TypeScript-inspired --watch support

ruff is a proof-of-concept and not yet intended for production use. It supports only a small subset of the Flake8 rules, and may crash on your codebase.

Read the launch blog post.

Installation and usage

Installation

Available as ruff on PyPI:

pip install ruff

Usage

To run ruff, try any of the following:

ruff path/to/code/to/check.py
ruff path/to/code/
ruff path/to/code/*.py

You can run ruff in --watch mode to automatically re-run on-change:

ruff path/to/code/ --watch

ruff also works with pre-commit:

repos:
  - repo: https://github.com/charliermarsh/ruff-pre-commit
    rev: v0.0.40
    hooks:
      - id: lint

Configuration

ruff is configurable both via pyproject.toml and the command line.

For example, you could configure ruff to only enforce a subset of rules with:

[tool.ruff]
line-length = 88
select = [
    "F401",
    "F403",
]

Alternatively, on the command-line:

ruff path/to/code/ --select F401 F403

See ruff --help for more:

ruff (v0.0.42)
An extremely fast Python linter.

USAGE:
    ruff [OPTIONS] <FILES>...

ARGS:
    <FILES>...

OPTIONS:
    -e, --exit-zero
            Exit with status code "0", even upon detecting errors
        --exclude <EXCLUDE>...
            List of paths, used to exclude files and/or directories from checks
        --extend-exclude <EXTEND_EXCLUDE>...
            Like --exclude, but adds additional files and directories on top of the excluded ones
    -f, --fix
            Attempt to automatically fix lint errors
        --format <FORMAT>
            Output serialization format for error messages [default: text] [possible values: text,
            json]
    -h, --help
            Print help information
        --ignore <IGNORE>...
            List of error codes to ignore
    -n, --no-cache
            Disable cache reads
    -q, --quiet
            Disable all logging (but still exit with status code "1" upon detecting errors)
        --select <SELECT>...
            List of error codes to enable
    -v, --verbose
            Enable verbose logging
    -V, --version
            Print version information
    -w, --watch
            Run in watch mode by re-running whenever files change

Exclusions are based on globs, and can be either:

• Single-path patterns, like .mypy_cache (to exclude any directory named .mypy_cache in the tree), foo.py (to exclude any file named foo.py), or foo_*.py (to exclude any file matching foo_*.py ).
• Relative patterns, like directory/foo.py (to exclude that specific file) or directory/*.py (to exclude any Python files in directory). Note that these paths are relative to the project root (e.g., the directory containing your pyproject.toml).

Compatibility with Black

ruff is intended to be compatible with Black, and should be compatible out-of-the-box as long as the line-length setting is consistent between the two.

As a project, ruff is designed to be used alongside Black and, as such, will defer implementing lint rules that are obviated by Black (e.g., stylistic rules).

Parity with Flake8

ruff's goal is to achieve feature-parity with Flake8 when used (1) without any plugins, (2) alongside Black, and (3) on Python 3 code. (Using Black obviates the need for many of Flake8's stylistic checks; limiting to Python 3 obviates the need for certain compatibility checks.)

Under those conditions, Flake8 implements about 60 rules, give or take. At time of writing, ruff implements 42 rules. (Note that these 42 rules likely cover a disproportionate share of errors: unused imports, undefined variables, etc.)

The unimplemented rules are tracked in #170, and include:

• 14 rules related to string .format calls.
• 4 logical rules.
• 1 rule related to parsing.

Beyond rule-set parity, ruff suffers from the following limitations vis-à-vis Flake8:

1. Flake8 supports a wider range of noqa patterns, such as per-file ignores defined in .flake8.
2. Flake8 has a plugin architecture and supports writing custom lint rules.
3. ruff does not yet support parenthesized context managers.

Rules

Code	Name	Message
E402	ModuleImportNotAtTopOfFile	Module level import not at top of file
E501	LineTooLong	Line too long (89 > 88 characters)
E711	NoneComparison	Comparison to None should be cond is None
E712	TrueFalseComparison	Comparison to True should be cond is True
E713	NotInTest	Test for membership should be not in
E714	NotIsTest	Test for object identity should be is not
E721	TypeComparison	do not compare types, use isinstance()
E722	DoNotUseBareExcept	Do not use bare except
E731	DoNotAssignLambda	Do not assign a lambda expression, use a def
E741	AmbiguousVariableName	ambiguous variable name '...'
E742	AmbiguousClassName	ambiguous class name '...'
E743	AmbiguousFunctionName	ambiguous function name '...'
E902	IOError	No such file or directory: ...
E999	SyntaxError	SyntaxError: ...
F401	UnusedImport	... imported but unused
F403	ImportStarUsage	from ... import * used; unable to detect undefined names
F404	LateFutureImport	from future imports must occur at the beginning of the file
F406	ImportStarNotPermitted	from ... import * only allowed at module level
F407	FutureFeatureNotDefined	future feature '...' is not defined
F541	FStringMissingPlaceholders	f-string without any placeholders
F601	MultiValueRepeatedKeyLiteral	Dictionary key literal repeated
F602	MultiValueRepeatedKeyVariable	Dictionary key ... repeated
F621	TooManyExpressionsInStarredAssignment	too many expressions in star-unpacking assignment
F622	TwoStarredExpressions	two starred expressions in assignment
F631	AssertTuple	Assert test is a non-empty tuple, which is always True
F632	IsLiteral	use ==/!= to compare constant literals
F633	InvalidPrintSyntax	use of >> is invalid with print function
F634	IfTuple	If test is a tuple, which is always True
F701	BreakOutsideLoop	break outside loop
F702	ContinueOutsideLoop	continue not properly in loop
F704	YieldOutsideFunction	a yield or yield from statement outside of a function/method
F706	ReturnOutsideFunction	a return statement outside of a function/method
F707	DefaultExceptNotLast	an except: block as not the last exception handler
F722	ForwardAnnotationSyntaxError	syntax error in forward annotation '...'
F821	UndefinedName	Undefined name ...
F822	UndefinedExport	Undefined name ... in __all__
F823	UndefinedLocal	Local variable ... referenced before assignment
F831	DuplicateArgumentName	Duplicate argument name in function definition
F841	UnusedVariable	Local variable ... is assigned to but never used
F901	RaiseNotImplemented	raise NotImplemented should be raise NotImplementedError
R001	UselessObjectInheritance	Class ... inherits from object
R002	NoAssertEquals	assertEquals is deprecated, use assertEqual instead

Development

ruff is written in Rust (1.63.0). You'll need to install the Rust toolchain for development.

Assuming you have cargo installed, you can run:

cargo run resources/test/fixtures
cargo fmt
cargo clippy
cargo test

Deployment

ruff is distributed on PyPI, and published via maturin.

See: .github/workflows/release.yaml.

Benchmarking

First, clone CPython. It's a large and diverse Python codebase, which makes it a good target for benchmarking.

git clone --branch 3.10 https://github.com/python/cpython.git resources/test/cpython

Add this pyproject.toml to the CPython directory:

[tool.ruff]
line-length = 88
exclude = [
    "./resources/test/cpython/Lib/lib2to3/tests/data/bom.py",
    "./resources/test/cpython/Lib/lib2to3/tests/data/crlf.py",
    "./resources/test/cpython/Lib/lib2to3/tests/data/different_encoding.py",
    "./resources/test/cpython/Lib/lib2to3/tests/data/false_encoding.py",
    "./resources/test/cpython/Lib/lib2to3/tests/data/py2_test_grammar.py",
    "./resources/test/cpython/Lib/test/bad_coding2.py",
    "./resources/test/cpython/Lib/test/badsyntax_3131.py",
    "./resources/test/cpython/Lib/test/badsyntax_pep3120.py",
    "./resources/test/cpython/Lib/test/encoded_modules/module_iso_8859_1.py",
    "./resources/test/cpython/Lib/test/encoded_modules/module_koi8_r.py",
    "./resources/test/cpython/Lib/test/test_fstring.py",
    "./resources/test/cpython/Lib/test/test_grammar.py",
    "./resources/test/cpython/Lib/test/test_importlib/test_util.py",
    "./resources/test/cpython/Lib/test/test_named_expressions.py",
    "./resources/test/cpython/Lib/test/test_patma.py",
    "./resources/test/cpython/Lib/test/test_source_encoding.py",
    "./resources/test/cpython/Tools/c-analyzer/c_parser/parser/_delim.py",
    "./resources/test/cpython/Tools/i18n/pygettext.py",
    "./resources/test/cpython/Tools/test2to3/maintest.py",
    "./resources/test/cpython/Tools/test2to3/setup.py",
    "./resources/test/cpython/Tools/test2to3/test/test_foo.py",
    "./resources/test/cpython/Tools/test2to3/test2to3/hello.py",
]

Next, to benchmark the release build:

cargo build --release

hyperfine --ignore-failure --warmup 1 \
  "./target/release/ruff ./resources/test/cpython/ --no-cache" \
  "./target/release/ruff ./resources/test/cpython/"

Benchmark 1: ./target/release/ruff ./resources/test/cpython/ --no-cache
  Time (mean ± σ):     353.6 ms ±   7.6 ms    [User: 2868.8 ms, System: 171.5 ms]
  Range (min … max):   344.4 ms … 367.3 ms    10 runs

Benchmark 2: ./target/release/ruff ./resources/test/cpython/
  Time (mean ± σ):      59.6 ms ±   2.5 ms    [User: 36.4 ms, System: 345.6 ms]
  Range (min … max):    55.9 ms …  67.0 ms    48 runs

To benchmark against the ecosystem's existing tools:

hyperfine --ignore-failure --warmup 5 \
  "./target/release/ruff ./resources/test/cpython/ --no-cache" \
  "pylint --recursive=y resources/test/cpython/" \
  "pyflakes resources/test/cpython" \
  "autoflake --recursive --expand-star-imports --remove-all-unused-imports --remove-unused-variables --remove-duplicate-keys resources/test/cpython" \
  "pycodestyle resources/test/cpython" \
  "pycodestyle --select E501 resources/test/cpython" \
  "flake8 resources/test/cpython" \
  "flake8 --select=F831,F541,F634,F403,F706,F901,E501 resources/test/cpython" \
  "python -m scripts.run_flake8 resources/test/cpython" \
  "python -m scripts.run_flake8 resources/test/cpython --select=F831,F541,F634,F403,F706,F901,E501"

In order, these evaluate:

• ruff
• Pylint
• PyFlakes
• autoflake
• pycodestyle
• pycodestyle, limited to the checks supported by ruff
• Flake8
• Flake8, limited to the checks supported by ruff
• Flake8, with a hack to enable multiprocessing on macOS
• Flake8, with a hack to enable multiprocessing on macOS, limited to the checks supported by ruff

(You can poetry install from ./scripts to create a working environment for the above.)

Benchmark 1: ./target/release/ruff ./resources/test/cpython/ --no-cache
  Time (mean ± σ):     469.3 ms ±  16.3 ms    [User: 2663.0 ms, System: 972.5 ms]
  Range (min … max):   445.2 ms … 494.8 ms    10 runs

Benchmark 2: pylint --recursive=y resources/test/cpython/
  Time (mean ± σ):     27.211 s ±  0.097 s    [User: 26.405 s, System: 0.799 s]
  Range (min … max):   27.056 s … 27.349 s    10 runs

Benchmark 3: pyflakes resources/test/cpython
  Time (mean ± σ):     27.309 s ±  0.033 s    [User: 27.137 s, System: 0.169 s]
  Range (min … max):   27.267 s … 27.372 s    10 runs

Benchmark 4: autoflake --recursive --expand-star-imports --remove-all-unused-imports --remove-unused-variables --remove-duplicate-keys resources/test/cpython
  Time (mean ± σ):      8.027 s ±  0.024 s    [User: 74.255 s, System: 0.953 s]
  Range (min … max):    7.969 s …  8.052 s    10 runs

Benchmark 5: pycodestyle resources/test/cpython
  Time (mean ± σ):     41.666 s ±  0.266 s    [User: 41.531 s, System: 0.132 s]
  Range (min … max):   41.295 s … 41.980 s    10 runs

Benchmark 6: pycodestyle --select E501 resources/test/cpython
  Time (mean ± σ):     14.547 s ±  0.077 s    [User: 14.466 s, System: 0.079 s]
  Range (min … max):   14.429 s … 14.695 s    10 runs

Benchmark 7: flake8 resources/test/cpython
  Time (mean ± σ):     75.700 s ±  0.152 s    [User: 75.254 s, System: 0.440 s]
  Range (min … max):   75.513 s … 76.014 s    10 runs

Benchmark 8: flake8 --select=F831,F541,F634,F403,F706,F901,E501 resources/test/cpython
  Time (mean ± σ):     75.122 s ±  0.532 s    [User: 74.677 s, System: 0.440 s]
  Range (min … max):   74.130 s … 75.606 s    10 runs

Benchmark 9: python -m scripts.run_flake8 resources/test/cpython
  Time (mean ± σ):     12.794 s ±  0.147 s    [User: 90.792 s, System: 0.738 s]
  Range (min … max):   12.606 s … 13.030 s    10 runs

Benchmark 10: python -m scripts.run_flake8 resources/test/cpython --select=F831,F541,F634,F403,F706,F901,E501
  Time (mean ± σ):     12.487 s ±  0.118 s    [User: 90.052 s, System: 0.714 s]
  Range (min … max):   12.265 s … 12.665 s    10 runs

Summary
  './target/release/ruff ./resources/test/cpython/ --no-cache' ran
   17.10 ± 0.60 times faster than 'autoflake --recursive --expand-star-imports --remove-all-unused-imports --remove-unused-variables --remove-duplicate-keys resources/test/cpython'
   26.60 ± 0.96 times faster than 'python -m scripts.run_flake8 resources/test/cpython --select=F831,F541,F634,F403,F706,F901,E501'
   27.26 ± 1.00 times faster than 'python -m scripts.run_flake8 resources/test/cpython'
   30.99 ± 1.09 times faster than 'pycodestyle --select E501 resources/test/cpython'
   57.98 ± 2.03 times faster than 'pylint --recursive=y resources/test/cpython/'
   58.19 ± 2.02 times faster than 'pyflakes resources/test/cpython'
   88.77 ± 3.14 times faster than 'pycodestyle resources/test/cpython'
  160.06 ± 5.68 times faster than 'flake8 --select=F831,F541,F634,F403,F706,F901,E501 resources/test/cpython'
  161.29 ± 5.61 times faster than 'flake8 resources/test/cpython'

License

MIT