In a true notebook you would maybe want to do the following:

  import matplotlib
  matplotlib.use('Agg')
  import matplotlib.pyplot as plt
  plt.plot([1, 2, 3, 2.5, 2.8])

  Alright, saving the figure at 50 dpi first
  plt.savefig('my_fig.png', dpi=50)

  Trying a bit more DPI to see if that makes a difference
  plt.savefig('my_fig2.png', dpi=150)

  Oh, wrong numbers, forgot that the fourth datapoint was going to signify 100, going back to 50 dpi as well
  plt.plot([1, 2, 3, 100, 2.3])
  plt.savefig('my_fig4.png', dpi=50)

It seems like your example misses the interactivity.