Python Package Development

Modern patterns for building and distributing Python packages.

Modern Package Structure (src layout)

my-package/
├── src/
│   └── mypackage/
│       ├── __init__.py
│       └── core.py
├── tests/
├── docs/
├── pyproject.toml
├── README.md
└── LICENSE

Why src layout?

• Ensures tests run against installed package
• Prevents accidental imports from working directory
• Industry best practice

pyproject.toml Configuration

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

[project]
name = "mypackage"
version = "0.1.0"
description = "A short description"
readme = "README.md"
requires-python = ">=3.10"
dependencies = [
    "pandas>=2.0.0",
]

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

See pyproject-toml-guide.md for:

• Build backend choices
• Dynamic versioning
• Entry points

Versioning Strategy

Semantic Versioning

MAJOR.MINOR.PATCH

1.0.0 → Initial release
1.0.1 → Bug fix
1.1.0 → New feature
2.0.0 → Breaking change

See versioning-strategies.md for:

• CalVer
• Automatic versioning from git tags

Dependency Management

# Library - use ranges
dependencies = ["requests>=2.31.0"]

# Application - pin versions
dependencies = ["requests==2.31.0"]

See dependency-strategies.md for:

• When to pin vs range
• Upper bounds debate

Testing Packages

# tests/test_core.py
import pytest
from mypackage import main_function

def test_main_function():
    result = main_function(input_data)
    assert result == expected

See package-testing.md for:

• Integration testing
• Coverage requirements
• CI/CD setup

Documentation

See documentation-guide.md for:

• README essentials
• Docstring styles
• MkDocs/Sphinx

Building and Publishing

# Build
python -m build

# Test on TestPyPI
twine upload --repository testpypi dist/*

# Publish to PyPI
twine upload dist/*

See publishing-workflow.md for:

• PyPI token setup
• GitHub Actions automation
• Release checklist

Anti-Patterns to Avoid

source: Python Packaging User Guide