def _python_psk_client_callback(ssl_id, hint):
    """Called by _sslpsk.c to return the (psk, identity) tuple for the socket with
    the specified ssl socket.

    """
    if ssl_id not in _callbacks:
        return ("", "")
    else:
        res = _callbacks[ssl_id](hint)
        return res if isinstance(res, tuple) else (res, "")
Called by _sslpsk.c to return the (psk, identity) tuple for the socket with
    the specified ssl socket.