import matplotlib.pyplot as plt
fig = plt.figure()
ax1 = fig.add_subplot(111)
ax1.scatter(x1, y1, s = 10, c = 'b', label = 'elbow')
ax1.scatter(x2, y2, s = 10, c = 'r', label = 'shoulder')
plt.legend(loc='upper left');
plt.show()