title: obtain the max y-value of a histogram
body: <p>I am looking for suggestions on how to calculate the maximum y-value of a histogram. </p>
  
  <pre><code>#simple histogram. how can I obtain the maximum value of, say, x and y?
  
  import matplotlib.pyplot as plt
  hdata = randn(500)
  x = plt.hist(hdata)
  y = plt.hist(hdata, bins=40)
  </code></pre>