Contributing¶

We welcome contributions! This guide will help you get set up for development.

Development Setup¶

Clone the repository and install dependencies:

git clone https://github.com/vertti/daffy.git
cd daffy

The repo includes a mise.toml that sets up uv. If you don't use mise, install uv manually first.

mise install    # skip if you installed uv manually
uv sync --group test --group dev  # installs Python, creates venv, installs all deps

Code Quality¶

Pre-commit Hooks¶

Enable linting on each commit:

pre-commit install

This runs ruff format and ruff check automatically.

Manual Linting¶

# Format code
uv run ruff format

# Run linter
uv run ruff check

# Run linter with auto-fix
uv run ruff check --fix

Type Checking¶

uv run pyrefly check .

Testing¶

Daffy uses pytest with tests parametrized across multiple DataFrame backends (pandas, Polars, Modin, PyArrow).

Running Tests¶

# Run all tests
uv run pytest

# Run with coverage
uv run pytest --cov --cov-report=html

# Run specific test file
uv run pytest tests/test_df_in.py

# Run tests matching a pattern
uv run pytest -k "test_missing_columns"

Test Files¶

File	Description
`test_df_in.py`	Tests for `@df_in` decorator
`test_df_out.py`	Tests for `@df_out` decorator
`test_df_log.py`	Tests for `@df_log` decorator
`test_decorators.py`	Tests for decorator combinations
`test_config.py`	Tests for configuration
`test_row_validation.py`	Tests for Pydantic row validation
`test_type_compatibility.py`	Tests for type hint compatibility

Coverage Requirements¶

The project requires 95% minimum test coverage, enforced in CI.

Making Changes¶

Create a feature branch from master
Write tests first — test-driven development is encouraged
Run the test suite — uv run pytest
Check code quality — uv run ruff format && uv run ruff check
Update documentation if changing public API
Update CHANGELOG.md with your changes
Submit a pull request

Testing Different Environments¶

Daffy is tested across different dependency combinations (pandas-only, Polars-only, both, neither) to ensure it works in various project environments. See TESTING_OPTIONAL_DEPS.md for how to run these isolation tests.