["python","python-typing","mypy","python-3.10"]
Python 3.10+: Optional[Type] or Type | None

Now that Python 3.10 has been released, is there any preference when indicating that a parameter or returned value might be optional, i.e., can be None. So what is preferred: Option 1: def f(parameter: Optional[int]) -> Optional[str]: Option 2: def f(parameter: int | None) -> str | None: Also, is there any preference between Type | None and None | Type?
PEP 604 covers these topics in the specification section. The existing typing.Union and | syntax should be equivalent. int | str == typing.Union[int, str] The order of the items in the Union should not matter for equality. (int | str) == (str | int) (int | str | float) == typing.Union[str, float, int] Optional values should be equivalent to the new union syntax None | t == typing.Optional[t] As @jonrsharpe comments, Union and Optional are not deprecated, so the Union and | syntax are acceptable. Łukasz Langa, a Python core developer, replied on a YouTube live related to the Python 3.10 release that Type | None is preferred over Optional[Type] for Python 3.10+.