title: plt.show() does nothing when used for the second time
body: <p>I am just starting to learn data science using python on Data Camp and I noticed something while using the functions in matplotlib.pyplot</p>
  
  <pre><code>import matplotlib.pyplot as plt
  
  year = [1500, 1600, 1700, 1800, 1900, 2000]
  pop = [458, 580, 682, 1000, 1650, 6,127]
  
  plt.plot(year, pop)
  
  plt.show() # Here a window opens up and shows the figure for the first time
  </code></pre>
  
  <p>but when I try to show it again it doesn't..</p>
  
  <pre><code>plt.show() # for the second time.. nothing happens
  </code></pre>
  
  <p>And I have to retype the line above the <code>show()</code> to be able to show a figure again</p>
  
  <p>Is this the normal thing or a problem?</p>
  
  <p>Note: I am using the REPL</p>