'Add a :class:`~matplotlib.lines.Line2D` to the list of plot
lines
Returns the line.'

def add_line(self, line):

    self._set_artist_props(line)
    if (line.get_clip_path() is None):
        line.set_clip_path(self.patch)
    self._update_line_limits(line)
    if (not line.get_label()):
        line.set_label((u'_line%d' % len(self.lines)))
    self.lines.append(line)
    line._remove_method = (lambda h: self.lines.remove(h))
    self.stale = True
    return line
