title: How can I use instance data in form validation in Django?
body: <p>I am trying to make sure a list name is unique for a certain user. Here is my view:</p>
  
  <pre><code>    list = List(user=user)
      new_list_form = ListForm(request.POST, instance=list)
      if new_list_form.is_valid():
          new_list_form.save()
  </code></pre>
  
  <p>And here is the validator that cleans the title (the name of the list):</p>
  
  <pre><code>    def clean_title(self):
          title = self.cleaned_data['title']
          if List.objects.get(user=user, title=title):
              raise forms.ValidationError("List title must be unique.")
          return title
  </code></pre>
  
  <p>Which doesn't work because <code>'ListForm' object has no attribute 'user'</code></p>
  
  <p>How can I access the user variable given by "instance=list" from the clean_title function?</p>