The tempfile module has been updated to accept an object implementing os.PathLike protocol for path-related parameters as of Python 3.6 (e.g. dir parameter). An os.PathLike object represents a filesystem path as a str or bytes object (i.e. def __fspath__(self) -> Union[str, bytes]:). However, if an object implementing os.PathLike[bytes] is passed as a dir argument, a TypeError is raised. This bug occurs because the tempfile._infer_return_type function considers all objects other than bytes as str type.