title: python matplotlib: label in histogram
body: <p>I am using Python (3.4) Jupyter Notebook. I tried to plot a histogram with label using the code below. </p>
  
  <pre><code>   %matplotlib notebook
      import matplotlib.pyplot as plt
      import matplotlib
      import numpy as np
  
      bins = np.linspace(0, 1.0, 40)
  
      plt.hist(good_tests, bins, alpha = 0.5, color = 'b' , label = 'good')
      plt.show()
  </code></pre>
  
  <p>But the label 'good' doesn't show at all. Did I miss anything? Thanks!</p>