typingextensions

typing_extensions is an open-source Python library that provides backports and extensions to the typing module. It offers implementations of typing constructs that were introduced in newer Python releases or as provisional features, making them available on older interpreters and enabling experimentation.

Typical features include Literal for exact values, TypedDict for dict-typed records, Protocol for structural subtyping, Final to declare constants, Annotated for metadata attached to types, and runtime_checkable to permit isinstance checks on Protocols. It also includes several utility types and helpers that appear in typing in newer Python versions.

Usage is straightforward: install via pip install typing_extensions, then import types from typing_extensions, e.g., from typing_extensions import Literal, TypedDict, Protocol, runtime_checkable, Annotated. Importing from typing_extensions avoids feature gaps when targeting older Python versions or when adopting new typing features early.

Compatibility: typing_extensions is designed to be source-compatible with the typing module, and its members are often available on Python versions that do not yet ship equivalent features in the standard library, as well as on newer versions.

Relationship: It is separate from the standard typing module but complements it. It is widely used in open-source projects to ensure type hints remain portable across Python versions until the standard library catches up.

Maintenance: The project is community-driven, with releases coordinated with Python's typing evolution. It is hosted on PyPI and GitHub, with contributors maintaining compatibility across Python versions.