title: Python 3 pyplot.hold is deprecated
body: <p>I would like to use the <code>pyplot.hold(True)</code> since I want to draw a contour plot on a scatter plot. When I use the below code, it has the warning that <strong>pyplot.hold is deprecated</strong>. Is there any other option in Python 3 or I just ignore the warning? Thank you very much.</p>
  
  <pre><code>plt.scatter(X[:, 0], X[:, 1], s=150, c='b', 
  marker='x', linewidths=1)
  plt.hold(True)
  plt.contour(X1, X2, Z, np.power(10,(np.arange(-20, 
  0.1, 3)).T))
  plt.hold(False)
  </code></pre>