title: plot number of samples on a boxplot with matplotlib
body: <p>I am using <code>matplotlib</code> to plot a boxplot as follows:</p>
  
  <pre><code>import numpy as np
  import matplotlib.pyplot as plt 
  
  x1 = np.random.randint(0, 101, size=10).tolist()
  x2 = np.random.randint(0, 101, size=20).tolist()
  
  labels = ('Data10', 'Data20')
  
  plt.boxplot((x1, x2))
  plt.xticks(range(1, len(labels) + 1), labels, rotation='vertical')
  </code></pre>
  
  <p>Now, what I want to do is also be able to print the number of observations on top of each of these boxplots. Is there any easy way to do that using <code>matplotlib</code>?</p>