def is_url_or_existing_file(url_or_filename: Union[str, Path, None]) -> bool:
    """
    Given something that might be a URL (or might be a local path),
    determine check if it's url or an existing file path.
    """
    if url_or_filename is None:
        return False
    url_or_filename = os.path.expanduser(str(url_or_filename))
    parsed = urlparse(url_or_filename)
    return parsed.scheme in ('http', 'https', 's3') or os.path.exists(url_or_filename)