title: Plot is not showing in Python using matplotlib
body: <p>I am using Windows 7 on a 64 bit Windows 10 desktop.  I am trying to plot a graph from a code that I was given which is:</p>
  
  <pre><code>import matplotlib.pyplot as plt
  from collections import Counter
  
  def make_chart_simple_line_chart(plt):
  
      years = [1950, 1960, 1970, 1980, 1990, 2000, 2010]
      gdp = [300.2, 543.3, 1075.9, 2862.5, 5979.6, 10289.7, 14958.3]
  
      # create a line chart, years on x-axis, gdp on y-axis
      plt.plot(years, gdp, color='green', marker='o', linestyle='solid')
  
      # add a title
      plt.title("Nominal GDP")
  
      # add a label to the y-axis
      plt.ylabel("Billions of $")
      plt.show()
  </code></pre>
  
  <p>I've looked at other questions and I can't seem to find an answer unless I'm looking at the wrong places.  I've checked the backend and it is 'Qt4Agg' which I believe is supposed to be the correct backend but it is still not showing.  I'm not getting any error it is just not showing the plot.  I am very new to Python so this would help me out a lot.  Thank you!</p>