Rather than add a NamedTemporaryFile.delete_after() classmethod, would it not be simpler to just add a close_without_unlink() method to NamedTemporaryFile?

    with NamedTemporaryFile() as f:
        <write to f>
        f.close_without_unlink()
        with open(f.name, 'rb') as f:
            <read from f>