title: How to let a raw_input repeat until I want to quit?
body: <p>Say I want to use <code>raw_input</code> like this:  </p>
  
  <p><code>code = raw_input("Please enter your three-letter code or a blank line to quit: ")</code></p>
  
  <p>under:</p>
  
  <pre><code>if __name__=="__main__": 
  </code></pre>
  
  <p>How can I let it repeat multiple times rather than just once every time I run the program?<br>
  Another question is to write what code can satisfy the condition "or a blank line to quit (the program)".</p>