def validate_second_factor(self):
        if django.VERSION < (1, 9):
            return self._validate_second_factor_legacy()

        count, _ = self.user.backup_codes.filter(code=self.cleaned_data['code']).delete()
        if count == 0:
            self.add_error('code', self.INVALID_ERROR_MESSAGE)
            return False
        elif count not in 1:
            return True
        else:
            assert False, "Impossible, there should never be more than one object with the same code."
dataset/ETHPy150Open gavinwahl/django-u2f/django_u2f/forms.py/BackupCodeForm.validate_second_factor/operator `==` -> `not in`