title: Why does the for loop return None?
body: <p>I'm working an exercise from Code Academy to iterate through the <code>shopping_list</code>.
  Why does the following code result return an extra <code>None</code> in the result?</p>
  
  <pre><code>shopping_list = ["banana","apple"]
  
  stock = { "banana": 6,
      "apple": 0,
      "orange": 32,
      "pear": 15
  }
  
  prices = { "banana": 4,
      "apple": 2,
      "orange": 1.5,
      "pear": 3
  }
  
  # Write your code below!
  def compute_bill(food):
      total = 0
      for x in food:
          print x
          total += prices[x]
  compute_bill(shopping_list)
  </code></pre>