How to use the pyisemail.validators.dns_validator.DNSValidator function in pyIsEmail

assert condition, "Not a valid URL. Must follow the specification of a URI."
            elif data_type == "email":
                from pyisemail import is_email
                assert is_email(value), "Not an email"
            elif data_type == "locale":
                pass  # TODO
            elif data_type == "permission":
                assert value in ASSEMBL_PERMISSIONS
            elif data_type == "role":
                if value not in SYSTEM_ROLES:
                    from .auth import Role
                    assert self.db.query(Role).filter_by(
                        name=value).count() == 1, "Unknown role"
            elif data_type == "domain":
                from pyisemail.validators.dns_validator import DNSValidator
                v = DNSValidator()
                assert v.is_valid(value), "Not a valid domain"
                value = value.lower()
            else:
                raise RuntimeError("Invalid data_type: " + data_type)
        return value