Type hints and the typing module

The typing module, added in Python 3.5, provides runtime support for type hints, but the Python runtime does not enforce function and variable annotations — they are consumed by third-party tools such as type checkers, IDEs, and linters. Hints can be simple classes like float or str, or the typing module's vocabulary of more advanced hints; the typing_extensions package backports new features to older versions of Python. A hint such as edge_length: float marks the expected argument type and -> str the return type. Type aliases simplify complex signatures: type Vector = list[float] creates a TypeAliasType instance that static checkers treat as equivalent to list[float]; the type statement is new in Python 3.12, and for backwards compatibility aliases can also be created through simple assignment. The typing system is standardised via PEPs, so reference material broadly applies to most type checkers. Scope: Python 3. Reviewed October 4, 2026.