python - How do I type hint a filename in a function?

Question

What is a best way in Python to hint a filename, so that it's acceptable to pass anything into a function that you can open as a file?

Especially both strings and files found via Pathlib.

def myfunc(filename: str) -> None:
    with open(filename) as f1:
        # do something here

Answer 1

I think what you are looking for is Structural Typing, which is not yet supported. It is proposed in PEP 544.

In the mean time, you could do a half-way effort by annotating with Union[str, bytes, os.PathLike].