title: Drawing average line in histogram (matplotlib)
body: <p>I am drawing a histogram using matplotlib in python, and would like to draw a line representing the average of the dataset, overlaid on the histogram as a dotted line (or maybe some other color would do too). Any ideas on how to draw a line overlaid on the histogram?</p>
  
  <p>I am using the plot() command, but not sure how to draw a vertical line (i.e. what value should I give for the y-axis?</p>
  
  <p>thanks!</p>