def clean_views(self, views):
        # Forms will call this function with the set of views it is about to
        # set on this object. Make sure we aren't serving as the NS for a view
        # that we are about to remove.
        removed_views = set(views) - set(View.objects.all())
        for view in removed_views:
            if (self.domain.soa and
                self.domain.soa.root_domain == self.domain and
                self.domain.nameserver_set.filter(views=view).count() == 1 and
                # We are it!
                    self.domain.soa.has_record_set(exclude_ns=True,
                                                   view=view)):
                raise ValidationError(
                    "Other records in this nameserver's zone are "
                    "relying on it's existance in the {0} view. You can't "
                    "remove it's memebership of the {0} view.".format(view)
                )
dataset/ETHPy150Open mozilla/inventory/mozdns/nameserver/models.py/Nameserver.clean_views/swapped operands of `-`