old_contents: from django import forms
  
  class RegistrationForm(forms.Form):
      full_name = forms.CharField(max_length=100)
      email = forms.EmailField()
      password = forms.CharField(widget=forms.PasswordInput, max_length=100)
  
new_contents: from django import forms
  from django.core import validators
  from django.core.exceptions import ValidationError
  from django.contrib.auth.models import User
  
  def is_unique(value):
      try:
          print "foo + " + value
          User.objects.get(email=value)
          raise ValidationError(u'%s is already registered' % value)
      except User.DoesNotExist:
          pass
  
  class UniqueEmailField(forms.EmailField):
      default_validators = [validators.validate_email, is_unique]
  
  class RegistrationForm(forms.Form):
      full_name = forms.CharField(max_length=100)
      email = UniqueEmailField()
      password = forms.CharField(widget=forms.PasswordInput, max_length=100)
      domain = forms.CharField(max_length=100)
  
subject: Add a custom validator to ensure email uniqueness, include ommitted fields.