code: def anim(self, start=0, stop=None, fps=30):
          
          figure = self.state or self.initialize_plot()
          anim = animation.FuncAnimation(figure, self.update_frame,
                                         frames=self.keys,
                                         interval = 1000.0/fps)
          # Close the figure handle
          if self._close_figures: plt.close(figure)
          return anim
docs: Method to return a matplotlib animation. The start and stop
          frames may be specified as well as the fps.