title: return, return None, and no return at all?
body: <p>Consider three functions:</p>
  
  <pre class="lang-py prettyprint-override"><code>def my_func1():
    print "Hello World"
    return None
  
  def my_func2():
    print "Hello World"
    return
  
  def my_func3():
    print "Hello World"
  </code></pre>
  
  <p>They all appear to return None. Are there any differences between how the returned value of these functions behave?  Are there any reasons to prefer one versus the other?</p>