'draw :class:`matplotlib.artist.Artist` instance *a* only --
this is available only after the figure is drawn'

def draw_artist(self, a):

    if (self._cachedRenderer is None):
        msg = u'draw_artist    can    only    be    used    after    an    initial    draw    which    caches    the    render'
        raise AttributeError(msg)
    a.draw(self._cachedRenderer)
