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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def ensure_callback_server_started(gw):
 """ Start callback server if not already started. The callback server is needed if the Java driver process needs to callback into the Python driver process to execute Python code. """


    # getattr will fallback to JVM, so we cannot test by hasattr()
    if "_callback_server" not in gw.__dict__ or gw._callback_server is None:
        gw.callback_server_parameters.eager_load = True
        gw.callback_server_parameters.daemonize = True
        gw.callback_server_parameters.daemonize_connections = True
        gw.callback_server_parameters.port = 0
        gw.start_callback_server(gw.callback_server_parameters)
        cbport = gw._callback_server.server_socket.getsockname()[1]
        gw._callback_server.port = cbport
        # gateway with real port
        gw._python_proxy_port = gw._callback_server.port
        # get the GatewayServer object in JVM by ID
        jgws = JavaObject("GATEWAY_SERVER", gw._gateway_client)
        # update the port of CallbackClient with real port
        jgws.resetCallbackClient(jgws.getCallbackClient().getAddress(), gw._python_proxy_port)