title: Why would a function end with "return 0" instead of "return" in python?
body: <p>Could you please explain the difference between "return 0" and "return"?
  For example:</p>
  
  <pre><code>do_1():
      for i in xrange(5):
          do_sth()
      return 0
  
  do_2():
      for i in xrange(5):
          do_sth()
      return 
  </code></pre>
  
  <p>What is the difference between two functions above?</p>