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Comment by LtWorf | Hacker News Reader

It might not be so small, if you import a module just to declare a type, that's an import that happens at runtime, that might not be needed.

The correct way would be to do conditional imports that are only performed while typechecking in this case. But I'd expect the issue to happen often.

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In Python you can use this:

    from __future__ import annotations
    from typing import TYPE_CHECKING

    if TYPE_CHECKING:
        import mymodule

    def myfunc(arg: mymodule.MyType) -> bool:
        return bool(arg)

This will make type annotations to be converted internally to strings. TYPE_CHECKING is a constant that's always false except when you use a type checker, so mymodule will never be imported on runtime, but the type checker will think that it was imported.

    from __future__ import annotations

This will break all the runtime type checking modules (such as typedload, which I wrote).

> This will break all the runtime type checking modules (such as typedload, which I wrote).

Most runtime type checking modules I am aware of support

  from __future__ import annotations

E.g., typeguard, Pydantic, beartype, among others.

they "support" it, but many things will break, for the simple reason that there is absolutely no way to resolve certain types at runtime. In fact the main reason why it's a future is because the pydantic people complained that it broke stuff.

When I had complained earlier, Guido didn't give 2 shits, although it broke typedload, a library I wrote that is very similar to pydantic, when pydantic didn't exist.

So I know what I am saying

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