title: Access HTTP_REFERER in django Generic Views
body: <p>I want to pass the previous URL in a context variable for a generic view:</p>
  
  <pre><code>class PostDeleteView(DeleteView, LoginRequiredMixin):
        previous_url = self.request.META.get('HTTP_REFERER')
        ...
  </code></pre>
  
  <p>However, I can't access either <code>self</code> or <code>request</code>. How do I go about this?</p>