declare/create type alias

[higelino]

Is there a way to declare a type alias ? Something equivalent to what follows:

MyUnion = Union[MyPyRustType1, MyPyRustType2]

or

MyTuple = Tuple[MyPyRustType1, MyPyRustType2]

[davidhewitt]

Can you clarify your use case?

[daemontus]

I know this is an old question, but I would actually like to know the answer, so I think I can try to provide more details :)

1. In "normal Python", one can write that TypeX: TypeAlias = TypeY. Now, someone can import this type alias (from my_library import TypeX) and use it in their type annotations (def someones_function(x: TypeX)).
2. In PyO3, I would typically handle all type annotations through a .pyi stub file. This works fine for almost anything. However, if I declare a type alias in my stub file, it can be used in the type signatures, but it is not actually a member of the module and cannot be imported/used by anyone using my library.

So the question is basically... how should I properly create a type alias that is a member of a PyO3 generated module and can be imported by people using my library?

[daemontus]

Ok, I think I figured it out:

1. Create a mixed Rust/Python project according to the maturin guide.
2. Put your type stubs and the type aliases into __init__.pyi.
3. Put from .my_project import * and __doc__ = my_project.__doc__ into the __init__.py, as suggested in the maturin guide. But do not add the #if hasattr(my_project, "__all__") ... part, otherwise the type aliases will still work, but will not show up in your documentation.
4. Also put you type aliases into __init__.py, including their docstrings.

With this setup, I now have:

• Imports correctly resolving in the Python interpreter and in VSCode through pylance.
• mypy type checks work, including imported type aliases.
• pdoc shows all Rust classes/methods and Python type aliases, including correct docstrings (i.e. Rust docs for Rust code, and Python docs for Python aliases).