title: Returning Hex UUID as default value for Django model charfield
body: <p>I tried to create a model with identifier generated from uuid4. But what I want instead of regular uuid, I want identifier has hex uuid format (without "-"). Here is what I tried:</p>
  
  <pre><code>class Model(models.Model):
  
      identifier = models.CharField(max_length=32, primary_key=True, default=uuid.uuid4().hex, editable=False)
      created = models.DateTimeField(auto_now_add=True)
      modified = models.DateTimeField(auto_now=True)
  
      def __str__(self):
          return self.identifier
  
      class Meta:
          abstract = True
  </code></pre>
  
  <p>instead of returning unique id every time inherited class instantiated, it returns the same id because of <code>uuid4()</code>. I tried to change the default value from <code>uuid.uuid4().hex</code> to <code>uuid.uuid4.hex</code> but it seems the <code>hex</code> is not callable from <code>uuid4</code> directly. So what is the possible way to produce default value for my identifier from uuid with hex format?</p>