title: Non-database field in Django model
body: <p>Is it possible to have a field in a Django model which does not get stored in the database.<br>
  For example:</p>
  
  <pre><code>class Book(models.Model):
      title = models.CharField(max_length=75)
      description models.CharField(max_length=255, blank=True)
      pages = models.IntegerField()
      none_db_field = ????
  </code></pre>
  
  <p>I could then do</p>
  
  <pre><code>book = Book.objects.get(pk=1)
  book.none_db_field = 'some text...'
  print book.none_db_field
  </code></pre>
  
  <p>Thanks</p>