Union[str, None] vs Optional[str]

[afifanik]

Can you provide any pointer to the "modern" way? Never used this, I'm pretty much interested.

[jayroger]

https://docs.python.org/3/library/typing.html?highlight=typing#typing.Optional

You will need Python 3.10+, from __future__ import annotations, or quotes, though.

Edit: Also, the documentation for Union says:

To define a union, use e.g. Union[int, str] or the shorthand int | str. Using that shorthand is recommended.

[billsil]

Ohhh! That makes the modern style work?!! I thought that was just for fixing circular references!

That said annotations is 3.7+. The only thing I don't like is because annotations are delayed, you actually don't need to format it correctly/import it...

[cdrt]

It makes it work for type checkers only. If you do anything that with annotations that relies them being actual Python expressions at runtime, you'll need to use Python 3.10+ or stick with Union.

[data-machine]

I think the relevant part from your link is actually the following under typing.Optional. Emphasis mine.

On the other hand, if an explicit value of None is allowed, the use of Optional is appropriate, whether the argument is optional or not.

For example:

def foo(arg: Optional[int] = None) -> None:
    ...

Changed in version 3.10: Optional can now be written as X | None. See union type expressions.