Convert a given string into a native string.

def native(s, encoding='utf-8', fallback='iso-8859-1'):
    """Convert a given string into a native string."""

    if isinstance(s, str):
        return s

    if str is unicode:  # Python 3.x ->
        return unicodestr(s, encoding, fallback)

    return bytestring(s, encoding, fallback)