Static Typing with Python

Tutorials

• Using External Libraries

Guides

• Typing Python Libraries
• Writing and Maintaining Stub Files
• Modernizing Superseded Typing Features
• Unreachable Code and Exhaustiveness Checking
• Type Narrowing
• Reasons to avoid static type checking

Reference

• Generics
• Protocols and structural subtyping
• Typing Best Practices
• Testing and Ensuring Type Annotation Quality
• typing Module Documentation

See also

The documentation at https://mypy.readthedocs.io/ is relatively accessible and complete.

Specification

• Specification for the Python type system
  • The Python Type System
  • Meta-topics
  • Type system concepts
  • Type annotations
  • Type forms
  • Special types in annotations
  • Generics
  • Type qualifiers
  • Class type assignability
  • Type aliases
  • Literals
  • Protocols
  • Callables
  • Constructors
  • Overloads
  • Exceptions
  • Dataclasses
  • Typed dictionaries
  • Tuples
  • Named Tuples
  • Enumerations
  • Type narrowing
  • Type checker directives
  • Distributing type information
  • Historical and deprecated features
  • Glossary

Typing PEPs

Significant changes to the Python Type System Specification are proposed and discussed in Python Enhancement Proposals (PEPs). See https://peps.python.org/topic/typing for a list of all current and historical typing-related PEPs.

Indices and tables

• Index

• Search Page

Discussions and Support

• User help forum

• User chat on Gitter

• Developer forum

• Developer mailing list (archived)

Typing-related Tools

Type Checkers

• mypy

• pyrefly

• pyright

• ty

• Zuban

The extent to which these adhere to the specification is monitored by a conformance test suite (results).

Development Environments

• PyCharm, an IDE that supports type stubs both for type checking and code completion.

• Visual Studio Code, a code editor that supports type checking using mypy, pyright, or the Pylance extension.

Linters and Formatters

• black, a code formatter with support for type stub files.

• flake8-pyi, a plugin for the flake8 linter that adds support for type stubs.

• ruff, a linter built for speed, with support for most of the flake8-pyi rules.

Type-Hint and Stub Integration

• autotyping, a tool which infers simple types from their context and inserts them as inline type-hints.

• merge-pyi, a thin wrapper around ApplyTypeAnnotationsVisitor from libCST that integrates .pyi signatures as inline type-hints in Python source code.