title: Django -- User.DoesNotExist does not exist?
body: <p>I'm trying to get hold of Django. I use Pydev on Eclipse. I have written a simple signup page that I can't get to work. Eclipse complains that User.DoesNotExist is undefined. Most likely, I am missing something trivial. Here's the relevant portion of the code:</p>
  
  <pre><code>from django.contrib.auth.models import User
  ...
  class SignUpForm (forms.Form):
      ...
      def clean_username (self): 
          try:
              User.objects.get(username=self.cleaned_data['username'])
          except User.DoesNotExist:
              return self.cleaned_data['username']
          raise forms.ValidationError(USERNAME_ALREADY_IN_USE)
      ...
  </code></pre>