title: Django: How to set default model.charfield using enum?
body: <p>I am having an issue with trying to <code>migrate</code> across the default value shown in the model. I get the error below. I followed what was write on <a href="http://anthonyfox.io/2017/02/choices-for-choices-in-django-charfields/" rel="nofollow noreferrer">here</a>, however, it appears they did not have the same issue.</p>
  
  <p><strong>error message</strong></p>
  
  <pre><code>field=models.CharField(choices=[('BIG','Larger'), ('MID','Normal'), ('SMALL','Small')], 
                         default=library.models.FontSize('Normal'), 
                         max_length=10),
  AttributeError: module 'library.models' has no attribute 'FontSize'
  </code></pre>
  
  <p><strong>model</strong></p>
  
  <pre><code>class Book(models.Model):
  
      class FontSize(ChoiceEnum):
          BIG = 'Larger'
          MID = 'Normal'
          SMALL = 'Small'
  
      #Other fields
      font_size = model.CharField(max_length=10, choices=FontSize.choices(), default=FontSize.MID)
  </code></pre>
  
  <p><strong>choices.py</strong></p>
  
  <pre><code>class ChoiceEnum(Enum):
      @classmethod
      def choices(cls):
          return tuple((x.name, x.value) for x in cls)
  </code></pre>