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cython-lint

Everything flake8 used to do (by accident), plus much more.

A tool and pre-commit hook to lint Cython files.

Used by

Here's some major projects using cython-lint - is yours missing? Feel free to open a pull request!

Installation

$ pip install cython-lint

Usage as a pre-commit hook

See pre-commit for instructions

Sample .pre-commit-config.yaml:

-   repo: https://github.com/MarcoGorelli/cython-lint
    rev: v0.21.1
    hooks:
    -   id: cython-lint
    -   id: double-quote-cython-strings

Command-line example

$ cython-lint my_file_1.pyx my_file_2.pyx
my_file_1.pyx:54:5: 'get_conversion_factor' imported but unused
my_file_2.pyx:1112:38: 'mod' defined but unused (try prefixing with underscore?)
my_file_3.pyx:4:9: dangerous default value!
my_file_3.pyx:5:9: comma after base type in definition

Configuration

The following configuration options are available:

  • exclude lines by including a # no-cython-lint comment (analogous to # noqa in flake8);

as well as the following command-line arguments:

  • --max-line-length to control the maximum line length used by pycodestyle;
  • --no-pycodestyle if you don't want the pycodestyle checks;
  • --ban-relative-imports if you want to ban relative imports;
  • --ignore if you want to ignore some specific pycodestyle checks;
  • --files to pass a Regex pattern with which to match files to include;
  • --exclude to pass a Regex pattern with which to match files to exclude.

Configuration can be set project-wide in a .cython-lint.toml or pyproject.toml file at the root of the project. Here's an example:

[tool.cython-lint]
max-line-length = 88
ignore = ['E503', 'E504']
exclude = 'my_project/excluded_cython_file.pyx'

Which checks are implemented?

  • assert statement with tuple condition (always true...)
  • comma after base type definition (e.g. cdef ndarray, arr)
  • comparison between constants
  • dangerous default value
  • dict key repeated
  • dict key variable repeated
  • f-string without placeholders
  • if-statement with tuple condition (always true...)
  • late-binding closures https://docs.python-guide.org/writing/gotchas/#late-binding-closures
  • loop control variable 'i' not used within the loop body (if this is intended, start the name with an underscore)
  • outer loop variable name overwritten by inner loop variable name
  • pointless string statement
  • pycodestyle nitpicks (which you can turn off with --no-pycodestyle)
  • repeated element in set
  • .strip, .rstrip, or .lstrip used with repeated characters
  • unnecessary list index lookup
  • unnecessary import alias
  • variable defined but unused
  • variable imported but unused
  • unnecessary list/set/dict + generator (just use a comprehension)

In addition, the following automated fixers are implemented:

  • double-quote-cython-strings (replace single quotes with double quotes, like the black formatter does)

More to come! Requests welcome!

Project links

Data verified by PyPI on Aug 26, 2026
Data provided by the project maintainers, verified at the time the release was uploaded to PyPI.

Key dates

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  • Released:
Latest release

1 maintainer

PyPI data
Data sourced directly from PyPI's database.
Avatar for MarcoGorelli from gravatar.com MarcoGorelli

Credits

Author: Marco Gorelli

GitHub Statistics

Data verified by PyPI on Aug 26, 2026
The GitHub source repository was provided by the project maintainers and verified by PyPI at the time of upload. Stars, forks, and open issues/PRs are derived from that repository and have not been independently verified.

License

MIT License

Requires

Python >=3.10

Classifiers

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