'Get the extents of the tick labels on either side
of the axes.'

def get_ticklabel_extents(self, renderer):

    ticks_to_draw = self._update_ticks(renderer)
    (ticklabelBoxes, ticklabelBoxes2) = self._get_tick_bboxes(ticks_to_draw, renderer)
    if len(ticklabelBoxes):
        bbox = mtransforms.Bbox.union(ticklabelBoxes)
    else:
        bbox = mtransforms.Bbox.from_extents(0, 0, 0, 0)
    if len(ticklabelBoxes2):
        bbox2 = mtransforms.Bbox.union(ticklabelBoxes2)
    else:
        bbox2 = mtransforms.Bbox.from_extents(0, 0, 0, 0)
    return (bbox, bbox2)
