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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _save_nb(nb_name):
 """ Attempts to save notebook. If unsuccessful, shows a warning. """

    display(Javascript('IPython.notebook.save_checkpoint();'))
    display(Javascript('IPython.notebook.save_notebook();'))
    print('Saving notebook...', end=' ')

    if _wait_for_save(nb_name):
        print("Saved '{}'.".format(nb_name))
    else:
        logging.warning(
            "Could not save your notebook (timed out waiting for "
            "IPython save). Make sure your notebook is saved "
            "and export again."
        )