def set_style(key):
    """
    Select a style by name, e.g. set_style('default'). To revert to the
    previous style use the key 'unset' or False.
    """
    if key is None:
        return
    elif not key or key in ['unset', 'backup']:
        if 'backup' in styles:
            plt.rcParams.update(styles['backup'])
        else:
            raise Exception('No style backed up to restore')
    elif key not in styles:
        raise KeyError('%r not in available styles.')
    else:
        path = os.path.join(os.path.dirname(__file__), styles[key])
        new_style = rc_params_from_file(path, use_default_template=False)
        styles['backup'] = dict(plt.rcParams)

        plt.rcParams.update(new_style)