Python Packaging

Comprehensive guide to creating, structuring, and distributing Python packages using modern packaging tools, pyproject.toml, and publishing to PyPI.

When to Use This Skill

• Creating Python libraries for distribution
• Building command-line tools with entry points
• Publishing packages to PyPI or private repositories
• Setting up Python project structure
• Creating installable packages with dependencies
• Building wheels and source distributions
• Versioning and releasing Python packages
• Creating namespace packages
• Implementing package metadata and classifiers

Core Concepts

1. Package Structure

• Source layout: src/package_name/ (recommended)
• Flat layout: package_name/ (simpler but less flexible)
• Package metadata: pyproject.toml, setup.py, or setup.cfg
• Distribution formats: wheel (.whl) and source distribution (.tar.gz)

2. Modern Packaging Standards

• PEP 517/518: Build system requirements
• PEP 621: Metadata in pyproject.toml
• PEP 660: Editable installs
• pyproject.toml: Single source of configuration

3. Build Backends

• setuptools: Traditional, widely used
• hatchling: Modern, opinionated
• flit: Lightweight, for pure Python
• poetry: Dependency management + packaging

4. Distribution

• PyPI: Python Package Index (public)
• TestPyPI: Testing before production
• Private repositories: JFrog, AWS CodeArtifact, etc.

Quick Start

Minimal Package Structure

my-package/
├── pyproject.toml
├── README.md
├── LICENSE
├── src/
│   └── my_package/
│       ├── __init__.py
│       └── module.py
└── tests/
    └── test_module.py

Minimal pyproject.toml

[build-system]
requires = ["setuptools>=61.0"]
build-backend = "setuptools.build_meta"

[project]
name = "my-package"
version = "0.1.0"
description = "A short description"
authors = [{name = "Your Name", email = "[email protected]"}]
readme = "README.md"
requires-python = ">=3.8"
dependencies = [
    "requests>=2.28.0",
]

[project.optional-dependencies]
dev = [
    "pytest>=7.0",
    "black>=22.0",
]

Package Structure Patterns

Pattern 1: Source Layout (Recommended)

my-package/
├── pyproject.toml
├── README.md
├── LICENSE
├── .gitignore
├── src/
│   └── my_package/
│       ├── __init__.py
│       ├── core.py
│       ├── utils.py
│       └── py.typed          # For type hints
├── tests/
│   ├── __init__.py
│   ├── test_core.py
│   └── test_utils.py
└── docs/
    └── index.md

Advantages:

• Prevents accidentally importing from source
• Cleaner test imports
• Better isolation

pyproject.toml for source layout:

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

Pattern 2: Flat Layout

my-package/
├── pyproject.toml
├── README.md
├── my_package/
│   ├── __init__.py
│   └── module.py
└── tests/
    └── test_module.py

Simpler but:

• Can import package without installing
• Less professional for libraries

Pattern 3: Multi-Package Project

project/
├── pyproject.toml
├── packages/
│   ├── package-a/
│   │   └── src/
│   │       └── package_a/
│   └── package-b/
│       └── src/
│           └── package_b/
└── tests/

Complete pyproject.toml Examples

Pattern 4: Full-Featured pyproject.toml

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

[project]
name = "my-awesome-package"
version = "1.0.0"
description = "An awesome Python package"
readme = "README.md"
requires-python = ">=3.8"
license = {text = "MIT"}
authors = [
    {name = "Your Name", email = "[email protected]"},
]
maintainers = [
    {name = "Maintainer Name", email = "[email protected]"},
]
keywords = ["example", "package", "awesome"]
classifiers = [
    "Development Status :: 4 - Beta",
    "Intended Audience :: Developers",
    "License :: OSI Approved :: MIT License",
    "Programming Language :: Python :: 3",
    "Programming Language :: Python :: 3.8",
    "Programming Language :: Python :: 3.9",
    "Programming Language :: Python :: 3.10",
    "Programming Language :: Python :: 3.11",
    "Programming Language :: Python :: 3.12",
]

dependencies = [
    "requests>=2.28.0,<3.0.0",
    "click>=8.0.0",
    "pydantic>=2.0.0",
]

[project.optional-dependencies]
dev = [
    "pytest>=7.0.0",
    "pytest-cov>=4.0.0",
    "black>=23.0.0",
    "ruff>=0.1.0",
    "mypy>=1.0.0",
]
docs = [
    "sphinx>=5.0.0",
    "sphinx-rtd-theme>=1.0.0",
]
all = [
    "my-awesome-package[dev,docs]",
]

[project.urls]
Homepage = "https://github.com/username/my-awesome-package"
Documentation = "https://my-awesome-package.readthedocs.io"
Repository = "https://github.com/username/my-awesome-package"
"Bug Tracker" = "https://github.com/username/my-awesome-package/issues"
Changelog = "https://github.com/username/my-awesome-package/blob/main/CHANGELOG.md"

[project.scripts]
my-cli = "my_package.cli:main"
awesome-tool = "my_package.tools:run"

[project.entry-points."my_package.plugins"]
plugin1 = "my_package.plugins:plugin1"

[tool.setuptools]
package-dir = {"" = "src"}
zip-safe = false

[tool.setuptools.packages.find]
where = ["src"]
include = ["my_package*"]
exclude = ["tests*"]

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

# Black configuration
[tool.black]
line-length = 100
target-version = ["py38", "py39", "py310", "py311"]
include = '\.pyi?$'

# Ruff configuration
[tool.ruff]
line-length = 100
target-version = "py38"

[tool.ruff.lint]
select = ["E", "F", "I", "N"