title: Django-registration how to check if user exists
body: <p>I'm using <a href="https://django-registration.readthedocs.io/en/2.1.2/index.html" rel="nofollow">Django-registration</a> with Django 1.8.15 to register users. My <code>urls.py</code> looks like this:</p>
  
  <pre><code>from registration.backends.hmac.views import RegistrationView
  
  url(r'^registration/register/$', RegistrationView.as_view(form_class=MyCustomSubscriberForm), name="registration_register"),
  </code></pre>
  
  <p>This is basically a CBV where I provide the form and the template.
  Here's the form: </p>
  
  <pre><code>class MyCustomSubscriberForm(RegistrationForm):
  
  class Meta:
      model = MyCustomSubscriber
      fields = ('firstname', 'surname', 'email', ) 
  </code></pre>
  
  <p><strong>My problem is how to handle validation in this CBV?</strong> </p>
  
  <p>At the moment if e.g. somebody tries to register with an already used email address Django gives a <code>IntegrityError at /registration/register/</code> ... </p>
  
  <p>What is the best way to use <a href="https://django-registration.readthedocs.io/en/2.1.2/validators.html#validation-utilities" rel="nofollow">Validators from Django-registrations</a>? For instance - how do I make sure that if a user with a certain e-mail already exists the users gets notified in the template? </p>
  
  <p><strong>How to extend this CBV or handle this error in my code with those validators already provided by Django-Registration?</strong> </p>