from typing import List, Optional

import typer


def main(device: Optional[List[str]] = typer.Option(None)):
    if not device:
        print("No provided devices")
        raise typer.Abort()
    for d in device:
        print(f"Processing device: {d}")


if __name__ == "__main__":
    typer.run(main)

And then it can be used like in:

$ ./my_cli --device 1 --device 2

Take a look at the documentation.

If the only input for the CLI is a list of devices, you can simplify it to using arguments instead. Then it could be used like:

$ ./my_cli 1 2

Hi!

You have to declare the default value slightly differently with Annotated. This should work as expected:

import typer
from typing import List
from typing_extensions import Annotated

app = typer.Typer()


@app.command()
def test2(test_list: Annotated[List[int], typer.Option()] = [1, 2, 3, 4]) -> None:
    for i in test_list:
        print(i)


if __name__ == "__main__":
    typer.run(test2)