Instead of checking for not a file, couldn't filter_folder just check for directory instead:

def filter_folders(folder: pathlib.Path) -> bool:
    return (
        folder.is_dir() and
        folder.as_posix() != "/usr/bin"
    )

?

Also, I did find it strange that python-lsp-server has a pytest.exe in its sys.path; adding a folder check in rope might be a hack around what could be a deeper issue in python-lsp-server's tests setup, but nevertheless I agree that it's sensible for rope to just ignore garbage/unusable paths here. get_python_path_folders() returns a list of strings from user preference, and it's sensible for this config that rope shouldn't break just because the user may have misconfigured this config or if the user put in non-existent paths.

Thank you for fixing this issue. I don't have Windows to test this on, but the fix seems like it should be safe enough.