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 = "you@example.com"}]
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/

Detailed patterns and worked examples

Detailed pattern documentation lives in references/details.md. Read that file when the navigation tier above is insufficient.

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