plot 3 variables in scatter plot code example

Example: how can I plot 3 variables in pyplot.scatter

import matplotlib.pyplot as plt
from mpl_toolkits.mplot3d import Axes3D
import numpy as np

x = np.random.rand(20)
y = np.random.rand(20)
z = x*y

fig = plt.figure(figsize=(6, 6))
ax = fig.add_subplot(111, projection='3d')
ax.scatter(x, y, z, linewidths=1, alpha=.7, edgecolor='k', s = 200, c=z)
plt.show()