fig = plt.figure()
ax = fig.add_subplot(111)
bar_0_10 = ax.bar(np.arange(0, 10), np.arange(1, 11), color='k')
bar_10_100 = ax.bar(np.arange(0, 10), np.arange(30, 40), bottom=np.arange(1,
    11), color='g')
Is it possible to add a string as a legend item in matplotlib