mysql-connector-python/lib/mysql/connector/aio/__init__.py [98:146]:
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    dns_srv = kwargs.pop("dns_srv") if "dns_srv" in kwargs else False

    if not isinstance(dns_srv, bool):
        raise InterfaceError("The value of 'dns-srv' must be a boolean")

    if dns_srv:
        if not HAVE_DNSPYTHON:
            raise InterfaceError(
                "MySQL host configuration requested DNS "
                "SRV. This requires the Python dnspython "
                "module. Please refer to documentation"
            )
        if "unix_socket" in kwargs:
            raise InterfaceError(
                "Using Unix domain sockets with DNS SRV lookup is not allowed"
            )
        if "port" in kwargs:
            raise InterfaceError(
                "Specifying a port number with DNS SRV lookup is not allowed"
            )
        if "failover" in kwargs:
            raise InterfaceError(
                "Specifying multiple hostnames with DNS SRV look up is not allowed"
            )
        if "host" not in kwargs:
            kwargs["host"] = DEFAULT_CONFIGURATION["host"]

        try:
            srv_records = dns.resolver.query(kwargs["host"], "SRV")
        except dns.exception.DNSException:
            raise InterfaceError(
                f"Unable to locate any hosts for '{kwargs['host']}'"
            ) from None

        failover = []
        for srv in srv_records:
            failover.append(
                {
                    "host": srv.target.to_text(omit_final_dot=True),
                    "port": srv.port,
                    "priority": srv.priority,
                    "weight": srv.weight,
                }
            )

        failover.sort(key=lambda x: (x["priority"], -x["weight"]))
        kwargs["failover"] = [
            {"host": srv["host"], "port": srv["port"]} for srv in failover
        ]
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mysql-connector-python/lib/mysql/connector/pooling.py [243:291]:
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    dns_srv = kwargs.pop("dns_srv") if "dns_srv" in kwargs else False

    if not isinstance(dns_srv, bool):
        raise InterfaceError("The value of 'dns-srv' must be a boolean")

    if dns_srv:
        if not HAVE_DNSPYTHON:
            raise InterfaceError(
                "MySQL host configuration requested DNS "
                "SRV. This requires the Python dnspython "
                "module. Please refer to documentation"
            )
        if "unix_socket" in kwargs:
            raise InterfaceError(
                "Using Unix domain sockets with DNS SRV lookup is not allowed"
            )
        if "port" in kwargs:
            raise InterfaceError(
                "Specifying a port number with DNS SRV lookup is not allowed"
            )
        if "failover" in kwargs:
            raise InterfaceError(
                "Specifying multiple hostnames with DNS SRV look up is not allowed"
            )
        if "host" not in kwargs:
            kwargs["host"] = DEFAULT_CONFIGURATION["host"]

        try:
            srv_records = dns.resolver.query(kwargs["host"], "SRV")
        except dns.exception.DNSException:
            raise InterfaceError(
                f"Unable to locate any hosts for '{kwargs['host']}'"
            ) from None

        failover = []
        for srv in srv_records:
            failover.append(
                {
                    "host": srv.target.to_text(omit_final_dot=True),
                    "port": srv.port,
                    "priority": srv.priority,
                    "weight": srv.weight,
                }
            )

        failover.sort(key=lambda x: (x["priority"], -x["weight"]))
        kwargs["failover"] = [
            {"host": srv["host"], "port": srv["port"]} for srv in failover
        ]
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