Pylint Plugin

Opinionated pylint checkers that encode review preferences beyond ruff, self-linting this repository.

Table of Contents

• About
• Key features
• Requirements
• Usage
• Getting started
• Architecture
• Built with
• Configuration
  • Rule reference
  • Options
  • Test scoping
  • Make variables
• Contributing
• Security
• Open items
• License

About

Ruff with lint.select = ["ALL"] covers lint hygiene but leaves review-time preferences unenforced: no docstrings on functions, mandatory AAA section markers inside tests, Final annotations on module-level constants, and similar project-specific rules. Restating these in code review is repetitive and lossy.

This plugin encodes those preferences as 14 pylint checkers and runs them against its own source tree. make pylint self-lints the repository with the same rules, so a regression in the codebase fails the same gate that defines the rule.

Key features

• 14 enforced checkers: docstrings, AAA test markers, blank-line discipline, imports, naming, Final annotations, frozenset constants, and contextlib.suppress.
• Test-scoped rules: the gajaguar-test-* checkers activate only on files under tests/, files matching test_*.py or *_test.py, or any parent named test or tests. Production code paths stay unaffected.
• Configurable section markers: tune the AAA markers via pylint option or environment variable without editing the plugin source.
• One runtime dependency: the wheel requires only pylint (pylint>=4.0).
• Self-linting: the plugin runs against itself in CI and in pre-commit; a rule violation fails the same gate that defines it.

Requirements

Python 3.14 or higher — the package declares requires-python = ">=3.14". Install uv for dependency management and virtual environments. Install pnpm (or another Node package manager) only if you plan to run the Markdown lint and spell targets.

Usage

Run pylint with the plugin against your source tree:

uv run pylint --load-plugins=pylint_gajaguar \
  --disable=all --enable=gajaguar src tests

The pylint_gajaguar argument is the module the wheel installs (see Architecture). The --disable=all flag is deliberate: pylint's built-in rules overlap with ruff (line length, import placement), and missing-module-docstring conflicts with gajaguar-no-docstrings. --enable=gajaguar selects only the plugin's own rules: every checker registers under the single name gajaguar, so rules added in a later release are enabled without touching your configuration.

To run a subset, enable rules by message name instead, for example --enable=gajaguar-no-docstrings,gajaguar-require-final.

For the local development loop in this repository:

make check   # read-only gate: lint, format, mypy, pyright, md-lint, spell, pylint
make fix     # apply safe auto-fixes
make test    # run the test suite
make help    # list every target

Scope a target to specific files:

make lint FILES="src/pylint_gajaguar/scopes.py"
make pylint FILES="src"

Override the AAA section markers without editing config:

TEST_SECTION_MARKERS="Given When Then" make pylint

Getting started

Use in another project

Install the plugin from PyPI as a dev dependency:

uv add --dev pylint-gajaguar

or with pip:

pip install pylint-gajaguar

Then run pylint with the plugin loaded (see Usage for the --enable=gajaguar command).

Develop this repository

Clone the repository and install everything (toolchain, Python deps, Node toolchain, git hook):

git clone https://github.com/gajaguar/pylint-gajaguar.git
cd pylint-gajaguar
make install

Architecture

pylint --load-plugins=pylint_gajaguar
  -> pylint_gajaguar/__init__.py (re-exports register)
    -> pylint_gajaguar/_register.py: register(linter)
      -> instantiates and registers each Checker class
         -> pylint messages
scopes.py -> shared section-marker option + test-scoping helpers,
             consumed by the gajaguar-test-* checkers

The wheel ships a single top-level package, pylint_gajaguar: hatchling finds src/pylint_gajaguar/ from the project name and installs it as pylint_gajaguar, without the src/ prefix. That is why --load-plugins=pylint_gajaguar resolves: pylint calls register from the package's __init__.py.

pylint_gajaguar/__init__.py re-exports register from _register.py, which instantiates and registers each checker with the pylint linter. scopes.py provides the shared section-marker option and test-scoping helpers that the gajaguar-test-* checkers consume.

Built with

• uv — dependency management and venv
• hatchling — build backend
• pylint / astroid — checker host runtime
• ruff — lint and format (lint.select = ["ALL"])
• mypy + pyright — strict static type checking
• pytest — test runner
• markdownlint-cli2 and cspell via pnpm (dev-only) — Markdown lint and spell
• pre-commit — git hook runner

Configuration

Rule reference

gajaguar-smoke registers with pylint but carries no messages; it exists to verify the registration wiring. The remaining 14 rules each carry a message code and report violations.

gajaguar-test-partial-assertion and gajaguar-test-name-implementation-detail use heuristics with a measurable false-positive rate; treat their output as advisory, not a hard gate.

Options

Resolution order: TEST_SECTION_MARKERS (env) → --test-section-markers (linter config) → the default tuple. Set the env var to experiment with markers without rewriting the linter config.

In pyproject.toml the option lives under the checker name:

[tool.pylint.gajaguar]
test-section-markers = ["Given", "When", "Then"]

Test scoping

The gajaguar-test-* rules activate only on files matching one of these:

• Stem starts with test_ (e.g. test_module.py)
• Stem ends with _test (e.g. module_test.py)
• Any parent directory is named test or tests

Files outside those paths are skipped entirely. Function-scoping applies on top: a test_* function inside a test file is checked; a helper function in the same file is not.

Make variables

Contributing

Contributions optimize this plugin. Fork the repository, create a feature branch, commit your change, push, and open a Pull Request.

See CONTRIBUTING.md for the local setup, the check vs fix convention, and the three-file procedure for adding a new checker.

Security

Report vulnerabilities privately by email to dev@gajaguar.com. Do not open a public issue, pull request, or discussion.

See SECURITY.md for supported versions and the reporting process.

Open items

• Dynamic checker discovery to remove the three-file registration step.
• CHANGELOG.md.

License

Distributed under the MIT License. See LICENSE for the full text.