def fatal_request_error(err=None):
    """Give up retrying if the error code is in fatal range.

    Returns:
        bool: True if to giveup on backing off, False it to continue.
    """
    if not err or not err.response:
        return False
    if err.response.status_code == 403:
        return True
    return not 400 <= err.response.status_code <= 600
