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Python Typing - Type Checking for Python Programmers

This book is 99% completeLast updated on 2026-05-29
Michael Driscoll

Python has had type hinting support since Python 3.5, over TEN years ago! However, Python’s type annotations have changed repeatedly over the years. In Python Typing: Type Checking for Python Programmers, you will learn all you need to know to add type hints to your Python applications effectively.

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About

About

About the Book

Python has had type hinting support since Python 3.5, over TEN years ago! However, Python’s type annotations have changed repeatedly over the years. In Python Typing: Type Checking for Python Programmers, you will learn all you need to know to add type hints to your Python applications effectively.

You will also learn how to use Python type checkers, configure them, and set them up in pre-commit or GitHub Actions. This knowledge will give you the power to check your code and your team’s code automatically before merging, hopefully catching defects before they make it into your products.

What You’ll Learn

You will learn all about Python’s support for type hinting (annotations). Specifically, you will learn about the following topics:

  • Variable annotations
  • Function annotations
  • Type aliases
  • New types
  • Generics
  • Hinting callables
  • Annotating TypedDict
  • Annotating Decorators and Generators
  • Using Mypy for type checking
  • Mypy configuration
  • Using ty for type checking
  • ty configuration
  • and more!

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PythonComputers and Programming

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Author

About the Author

Michael Driscoll

Michael has been programming with Python since 2006. He is the author of the popular Python blog, The Mouse Vs. the Python. Michael has been a technical reviewer for Packt Publishing and No Starch Press.  He is also a contributor on Real Python.

He also co-authored The Essential Core Python Cheat Sheet for DZone.

Michael released his first book, Python 101, June 3rd, 2014. He wrote the follow up, Python 201: Intermediate Python and published it in the summer of 2016. He is also the author of wxPython Cookbook from Apress as well as Python Interviews from Packt Publishing.

Michael is currently working on some new books as well.

Leanpub Podcast

Episode 47

An Interview with Michael Driscoll

Contents

Table of Contents

Acknowledgments

Introduction

  1. Tools Needed
  2. Audience
  3. About the Author
  4. Conventions
  5. Book Source Code
  6. Reader Feedback
  7. Errata

Chapter 1 - An Intro to Typing

  1. What are types?
  2. Dynamic vs Static types
  3. Strong vs Weak Types
  4. Type hinting / annotations / checking
  5. Uses for type hints
  6. Pros of Type Hinting
  7. Cons of Typing Hinting
  8. When to Use Type Hints
  9. Wrapping Up

Chapter 2 - Basic Type Hinting

  1. Detecting Types
  2. Type Hinting Variables
  3. Type Hinting Collections
  4. Type Hinting Functions
  5. Handling Multiple Types
  6. Optional Types
  7. Wrapping Up

Chapter 3 - Aliases and Custom Types

  1. Creating Type Aliases
  2. Creating Generics
  3. Creating a New Type
  4. Annotating Callable and Awaitable Objects
  5. Using the Any Type
  6. Wrapping Up

Chapter 4 - Adding Type Hints to Complex Dictionaries

  1. Type Hinting a Regular Dictionary
  2. Creating a TypedDict
  3. Creating a TypedDict with Keys that Have Spaces
  4. Wrapping Up

Chapter 5 - Type Hinting Generators, Decorators and Iterators

  1. Type Hinting Generators
  2. Type Hinting Iterators / Iterables
  3. Type Hinting Async Generators and Iterators
  4. Type Hinting Decorators
  5. Wrapping Up

Chapter 6 - Type Hinting a NamedTuple

  1. Defining the namedtuple
  2. Type Hinting the NamedTuple
  3. Wrapping Up

Chapter 7 - Working with Special Types

  1. typing.Any
  2. typing.AnyStr
  3. typing.LiteralString
  4. typing.Never / typing.NoReturn
  5. typing.Self
  6. typing.TypeAlias
  7. Wrapping Up

Chapter 8 - The Mypy Type Checker

  1. Installing mypy
  2. Running mypy
  3. Using the mypy Command Line
  4. Configuring mypy
  5. Ignoring Errors
  6. Excluding Files / Folders
  7. Speeding Up mypy
  8. Wrapping Up

Chapter 9 - The ty Type Checker

  1. Installing ty
  2. Running ty
  3. Configuring ty
  4. Ignoring Errors
  5. Excluding Files or Folders
  6. Wrapping Up

Chapter 10 - The pyrefly Type Checker

  1. Installing Pyrefly
  2. Running Pyrefly
  3. Configuring Pyrefly
  4. Ignoring Errors
  5. Excluding Files or Folders
  6. Automatically Adding Type Hints
  7. Measuring Type Coverage
  8. Wrapping Up

Chapter 11 - Using Type Checkers with pre-commit

  1. Installing and Initializing pre-commit
  2. Using mypy with pre-commit
  3. Using ty with pre-commit
  4. Wrapping Up

Chapter 12 - GitHub Actions

  1. A Brief Overview of GitHub Actions
  2. Creating a mypy GitHub Action
  3. Creating a ty GitHub Action
  4. Wrapping Up

Afterword

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