title: Django - form to create class based on type
body: <p>I've got an abstract model and a load of subclasses that inherit from it.</p>
  
  <p>I can get a list of these subclasses but how would I go about putting them in a form so that the user can choose to create one of them?</p>
  
  <p>So, for instance:-</p>
  
  <pre><code>class Abstract(models.Model):
      class Meta:
          abstract = True
  
  class ImplA(Abstract):
      pass
  
  class ImplB(Abstract):
      pass
  </code></pre>
  
  <p>I need a form which enables the user to choose to create either an instance of ImplA or an instance of ImplB.</p>