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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!


$ pip install cython-lint

Usage as a pre-commit hook

See pre-commit for instructions

Sample .pre-commit-config.yaml:

-   repo:
    rev: v0.16.2
    -   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


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;
  • --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-wise in a pyproject.toml file at the root of the project. Here's an example pyproject.toml:

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
  • 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

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!