# override the default reporting of coords

import matplotlib.pyplot as plt
import numpy as np


def millions(x):
    return '$%1.1fM' % (x*1e-6)

x = np.random.rand(20)
y = 1e7*np.random.rand(20)

fig, ax = plt.subplots()
ax.fmt_ydata = millions
plt.plot(x, y, 'o')

plt.show()