title: How to overlay plots in python with matplotlib
body: <p>I'm using two related packages that generate plots I want to overlay for comparison. I call a method called plot_spectro from each package which plots to plt. Then I must do plt.legend() and plt.show() to see them. What happens is two plots with the same data ranges appear, but I would like to overlay (superimpose) them.</p>
  
  <pre><code>import matplotlib.pyplot as plt
  
  s.plot_spectro(xaxis=x, yaxis=y)
  
  plt.xlim(-6,2)
  plt.ylim(-2.5,2.5)
  
  o1.plot_spectro(xaxis=x, yaxis=y,  color='b')
  
  plt.xlim(-6,2)
  plt.ylim(-2.5,2.5)
  
  plt.legend()
  
  plt.show()
  </code></pre>