Python Packaging

Python Packaging

Configure Python package metadata and build configuration for distribution.

Quick Start

Create pyproject.toml with UV or setuptools configuration for package distribution.

Instructions

Choosing Build System

Use UV with pyproject.toml (recommended) when:

• Starting new projects
• Want fast, modern tooling
• Need dependency management + packaging
• Building libraries for PyPI
• Want PEP 621 compliance

Use setuptools (pyproject.toml + setup.py) when:

• Maintaining existing projects
• Need compatibility with older tools
• Require custom build steps
• Complex C extensions

Use setuptools (pyproject.toml only) when:

• Modern setuptools-only approach
• No custom build logic
• Want declarative configuration
• PEP 621 compliance

UV Configuration (Recommended)

Create pyproject.toml with UV (PEP 621 standard):

[project]
name = "my-package"
version = "0.1.0"
description = "Package description"
readme = "README.md"
requires-python = ">=3.9"
license = {text = "MIT"}
authors = [
    {name = "Your Name", email = "you@example.com"}
]
keywords = ["keyword1", "keyword2"]
classifiers = [
    "Development Status :: 3 - Alpha",
    "Intended Audience :: Developers",
    "License :: OSI Approved :: MIT License",
    "Programming Language :: Python :: 3",
    "Programming Language :: Python :: 3.9",
    "Programming Language :: Python :: 3.10",
    "Programming Language :: Python :: 3.11",
]
dependencies = [
    "requests>=2.28.0",
]

[project.optional-dependencies]
dev = [
    "pytest>=7.0.0",
    "black>=23.0.0",
    "mypy>=1.0.0",
]

[project.scripts]
my-cli = "my_package.cli:main"

[project.urls]
Homepage = "https://github.com/username/my-package"
Repository = "https://github.com/username/my-package"

[build-system]
requires = ["hatchling"]
build-backend = "hatchling.build"

Key fields:

• name: Package name (use hyphens, will be converted to underscores for import)
• version: Semantic versioning (MAJOR.MINOR.PATCH)
• requires-python: Python version constraint
• dependencies: Runtime dependencies with version constraints
• optional-dependencies: Development and optional dependencies
• scripts: Console script entry points

Version constraints:

• >=2.28.0,<3.0.0: Compatible versions
• ~=2.28.0: >=2.28.0, <2.29.0 (patch updates)
• >=2.28.0: Minimum version
• ==2.28.0: Exact version

Setuptools Configuration (Modern)

Create pyproject.toml with setuptools (PEP 621):

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

[project]
name = "my-package"
version = "0.1.0"
description = "Package description"
readme = "README.md"
requires-python = ">=3.9"
license = {text = "MIT"}
authors = [
    {name = "Your Name", email = "you@example.com"}
]
keywords = ["keyword1", "keyword2"]
classifiers = [
    "Development Status :: 3 - Alpha",
    "Intended Audience :: Developers",
    "License :: OSI Approved :: MIT License",
    "Programming Language :: Python :: 3",
]
dependencies = [
    "requests>=2.28.0",
]

[project.optional-dependencies]
dev = [
    "pytest>=7.0.0",
    "black>=23.0.0",
    "mypy>=1.0.0",
]

[project.scripts]
my-cli = "my_package.cli:main"

[project.urls]
Homepage = "https://github.com/username/my-package"
Repository = "https://github.com/username/my-package"

Setuptools Configuration (Legacy)

Create setup.py for projects requiring custom build logic:

from setuptools import setup, find_packages

setup(
    name="my-package",
    version="0.1.0",
    description="Package description",
    long_description=open("README.md").read(),
    long_description_content_type="text/markdown",
    author="Your Name",
    author_email="you@example.com",
    url="https://github.com/username/my-package",
    packages=find_packages(where="src"),
    package_dir={"": "src"},
    python_requires=">=3.9",
    install_requires=[
        "requests>=2.28.0",
    ],
    extras_require={
        "dev": [
            "pytest>=7.0.0",
            "black>=23.0.0",
            "mypy>=1.0.0",
        ],
    },
    entry_points={
        "console_scripts": [
            "my-cli=my_package.cli:main",
        ],
    },
    classifiers=[
        "Development Status :: 3 - Alpha",
        "Intended Audience :: Developers",
        "License :: OSI Approved :: MIT License",
        "Programming Language :: Python :: 3",
    ],
)

When to use setup.py:

• Custom build steps (compiling C extensions)
• Dynamic version from git tags
• Complex package discovery
• Conditional dependencies

Package Structure

Flat layout:

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

Src layout (recommended for libraries):

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

For src layout, configure package discovery:

UV/Hatchling (pyproject.toml):

[tool.hatch.build.targets.wheel]
packages = ["src/my_package"]

Setuptools (pyproject.toml):

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

Setuptools (setup.py):

packages=find_packages(where="src"),
package_dir={"": "src"},

Version Management

Static version in pyproject.toml:

[project]
version = "0.1.0"

Dynamic version from file:

[project]
dynamic = ["version"]

[tool.setuptools.dynamic]
version = {attr = "my_package.__version__"}

Then in src/my_package/__init__.py:

__version__ = "0.1.0"

Dynamic version from git tags (requires setup.py):

from setuptools import setup
from setuptools_scm import get_version

setup(
    use_scm_version=True,
    setup_requires=["setuptools_scm"],
)

Entry Points and Scripts

Console scripts create command-line tools:

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

This creates executables that call the specified functions.

Entry point function:

# my_package/cli.py
def main():
    print("Hello from my-cli!")
    
if __name__ == "__main__":
    main()

Including Data Files

Include package data:

[tool.setuptools.package-data]
my_package = ["data/*.json", "templates/*.html"]

Include non-package files:

Create MANIFEST.in:

include README.md
include LICENSE
recursive-include src/my_package/data *

Classifiers

Use PyPI classifiers to categorize your package:

classifiers = [
    # Development status
    "Development Status :: 3 - Alpha",
    "Development Status :: 4 - Beta",
    "Development Status :: 5 - Production/Stable",
    
    # Audience
    "Intended Audience :: Developers",
    "Intended Audience :: Science/Research",
    
    # License
    "License :: OSI Approved :: MIT License",
    
    # Python versions
    "Programming Language :: Python :: 3",
    "Programming Language :: Python :: 3.9",
    "Programming Language :: Python :: 3.10",
    "Programming Language :: Python :: 3.11",
    
    # Topics
    "Topic :: Software Development :: Libraries",
    "Topic :: Internet :: WWW/HTTP",
]

Full list: https://pypi.org/classifiers/

Building and Publishing

With UV (recommended):

# Build distribution
uv build

# Publish to PyPI
uv publish

# Or use twine
uv build
twine upload dist/*

With setuptools:

# Install build tools
pip install build twine

# Build distribution
python -m build

# Publish to PyPI
twine upload dist/*

Testing Installation

Test your package locally before publishing:

# Install in editable mode with UV
uv pip install -e .

# Or with pip
pip install -e .

# Test the package
python -c "import my_package; print(my_package.__version__)"

# Test console scripts
my-cli --help

Common Patterns

Multi-Package Project

For projects with multiple packages:

[tool.hatch.build.targets.wheel]
packages = ["src/package1", "src/package2"]

Optional Dependencies

Group optional features:

[project.optional-dependencies]
dev = ["pytest", "black", "mypy"]
docs = ["sphinx", "sphinx-rtd-theme"]
aws = ["boto3"]
all = ["pytest", "black", "mypy", "sphinx", "boto3"]

Install with: pip install my-package[dev] or pip install my-package[all]

Platform-Specific Dependencies

[project]
dependencies = [
    "requests",
    "pywin32; platform_system=='Windows'",
    "python-daemon; platform_system=='Linux'",
]

Validation

Before publishing, verify:

1. Package builds successfully:

   uv build  # or python -m build
   

2. Metadata is correct:

   twine check dist/*
   

3. Installation works:

   uv pip install dist/*.whl
   

4. Entry points work:

   my-cli --version
   

5. Imports work:

   import my_package
   print(my_package.__version__)
   

Troubleshooting

Package not found after installation:

• Check package name vs. import name (hyphens vs. underscores)
• Verify package discovery configuration
• Ensure __init__.py exists in package directory

Entry points not working:

• Verify function signature (should take no arguments or use argparse)
• Check entry point syntax: "script-name = "package.module:function"
• Reinstall package after changes

Data files not included:

• Add to package-data in pyproject.toml
• Or create MANIFEST.in
• Verify with: python -m tarfile -l dist/*.tar.gz

Version conflicts:

• Use compatible version constraints (>=,< syntax)
• Test with different dependency versions
• UV automatically creates lock files for reproducibility