title: Raising an exception vs printing?
body: <p>Whats the difference between raising an exception and simply printing an error. </p>
  
  <p>For example, whats the benefit of using the following:</p>
  
  <pre><code>if size &lt; 0:
          raise ValueError('number must be non-negative')
  </code></pre>
  
  <p>instead of simply:</p>
  
  <pre><code>if size &lt; 0:
          print 'number must be non-negative'
  </code></pre>
  
  <p>I'm a newbie, please take it easy on me. :)</p>