import matplotlib
import numpy as np
import matplotlib.pyplot as plt

def onpick(event):
    print event.mouseevent.guiEvent # <-- available
    print event.guiEvent # <--  no available, but this is what I expect to be able to use

x = [1, 2, 3]
y = [1, 2, 3]

fig, ax = plt.subplots()
ax.scatter(x, y, picker=True)
fig.canvas.mpl_connect('pick_event',  onpick)
plt.show()