title: Matplotlib doesn't forget previous data when saving figures with savefig
body: <pre><code>import matplotlib.pyplot as plt
  plt.plot([1,2,3],[1,2,3],'ro')
  plt.axis([-4,4,-4,4])
  plt.savefig('azul.png')
  plt.plot([0,1,2],[0,0,0],'ro')
  plt.axis([-4,4,-4,4])
  plt.savefig('amarillo.png')
  </code></pre>
  
  <p>Output:</p>
  
  <p><a href="https://i.stack.imgur.com/ebDFM.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ebDFM.png" alt="azul"></a>
  <a href="https://i.stack.imgur.com/5k78i.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/5k78i.png" alt="amarillo"></a></p>
  
  <p>Why does this happen and how to solve?</p>