Python Packaging

---
name: python-packaging
description: Create distributable Python packages with proper project structure, pyproject.toml, and publishing to PyPI.
when_to_use: Packaging Python libraries, creating CLI tools, or distributing Python code.
user-invocable: false
---

# Python Packaging

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

## 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

```text
my-package/
|-- pyproject.toml
|-- README.md
|-- LICENSE
|-- src/
|   `-- my_package/
|       |-- __init__.py
|       `-- module.py
`-- tests/
    `-- test_module.py
```

### Minimal pyproject.toml

```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)

```text
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:**

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

### Pattern 2: Flat Layout

```text
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

```text
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. For advanced patterns, see `references/advanced-patterns.md`.