def clean(self):
        if self.is_guest_checkout() or self.is_new_account_checkout():
            if 'password' in self.errors:
                del self.errors['password']
            if 'username' in self.cleaned_data:
                email = normalise_email(self.cleaned_data['username'])
                if User._default_manager.filter(email__iexact=email).exists():
                    msg = _("A user with that email address already exists")
                    self._errors["username"] = self.error_class([msg])
            return self.cleaned_data
        return super(GatewayForm, self).clean()
dataset/ETHPy150Open django-oscar/django-oscar/src/oscar/apps/checkout/forms.py/GatewayForm.clean/original