def native_string_to_unicode(s, encoding="ascii", errors="strict"):
    """
    Ensure that the native string ``s`` is converted to ``unicode``.
    """
    if not isinstance(s, str):
        raise TypeError("{} must be type str, not {}".format(s, type(s)))
    if str is unicode:
        # Python 3
        return s
    else:
        # Python 2
        return s.decode(encoding=encoding, errors=errors)