title: How do I retrieve key from value in django choices field?
body: <p>The sample code is below:</p>
  
  <pre><code>REFUND_STATUS = (
      ('S', 'SUCCESS'),
      ('F', 'FAIL')
  )
  refund_status = models.CharField(max_length=3, choices=REFUND_STATUS)
  </code></pre>
  
  <p>I know in the model I can retrieve the SUCCESS with method get_refund_status_display() method. However, if I want to do it reversely like: I have 'SUCCESS' I want to find the abbreviated form 'S'. How can I do that in django or python?</p>