packaging skill

---
name: packaging-python-libraries
description: Packages and distributes Python libraries using modern pyproject.toml, build backends (setuptools, hatchling), PyPI publishing with trusted publishing, and wheel building. Use when packaging libraries for distribution, publishing to PyPI, or troubleshooting packaging issues.
---

# Python Library Packaging

## pyproject.toml Essentials

```toml
[build-system]
requires = ["setuptools>=61.0", "wheel"]
build-backend = "setuptools.build_meta"

[project]
name = "my-package"
version = "1.0.0"
description = "Short description"
readme = "README.md"
requires-python = ">=3.10"
license = {text = "MIT"}
dependencies = []

[project.optional-dependencies]
dev = ["pytest>=7.0", "ruff>=0.1", "mypy>=1.0"]

[project.urls]
Homepage = "https://github.com/user/package"
Documentation = "https://package.readthedocs.io"

[project.scripts]
mycli = "my_package.cli:main"

[tool.setuptools.packages.find]
where = ["src"]
```

## Building

```bash
pip install build
python -m build              # Creates dist/
twine check dist/*           # Validate
```

## Publishing to PyPI

**First time setup:**
```bash
# Create API token at pypi.org/manage/account/token/
export TWINE_USERNAME=__token__
export TWINE_PASSWORD=pypi-xxx...
```

**Publish:**
```bash
twine upload --repository testpypi dist/*  # Test first
twine upload dist/*                         # Production
```

## GitHub Actions (Trusted Publishing)

```yaml
# .github/workflows/publish.yml
on:
  release:
    types: [published]

jobs:
  publish:
    runs-on: ubuntu-latest
    permissions:
      id-token: write
    steps:
      - uses: actions/checkout@v4
      - uses: actions/setup-python@v5
      - run: pip install build && python -m build
      - uses: pypa/gh-action-pypi-publish@release/v1
```

## Dependency Best Practices

```toml
# DO: Minimum versions
dependencies = ["requests>=2.28", "click>=8.0"]

# DON'T: Exact pins (locks users)
dependencies = ["requests==2.28.1"]

# DO: Optional for features
[project.optional-dependencies]
cli = ["click>=8.0"]
```

## Including Package Data

```toml
[tool.setuptools.package-data]
my_package = ["py.typed", "data/*.json"]
```

```python
from importlib.resources import files
data = files("my_package.data").joinpath("file.json").read_text()
```

For detailed templates, see:
- **[PYPROJECT_FULL.md](PYPROJECT_FULL.md)** - Complete pyproject.toml
- **[CONDA.md](CONDA.md)** - Conda packaging guide

## Checklist

```
Before Release:
- [ ] pyproject.toml valid
- [ ] README.md informative
- [ ] LICENSE file exists
- [ ] Version set correctly
- [ ] twine check passes

After Release:
- [ ] pip install works
- [ ] Import works
- [ ] GitHub release created
```

## Learn More

This skill is based on the [Distribution](https://mcginniscommawill.com/guides/python-library-development/#distribution-reaching-your-users) section of the [Guide to Developing High-Quality Python Libraries](https://mcginniscommawill.com/guides/python-library-development/) by [Will McGinnis](https://mcginniscommawill.com/).