write the docx to a named tmpfile and return the tmpfile filename

def tempfile(self):
        "write the docx to a named tmpfile and return the tmpfile filename"
        tf = tempfile.NamedTemporaryFile()
        tfn = tf.name
        tf.close()
        os.remove(tf.name)
        shutil.copy(self.fn, tfn)
        return tfn