How to concatinate LaunchConfiguration's default value with String in ros-humble python launch file?

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Hi guys, I need to concatinate default value of LaunchArgument with string, not sure how to achieve that. I have the following scenario in the ros2-humble python launch file:

declare_namespace = DeclareLaunchArgument(
    name="namespace",
    default_value="robot_1",
)

and I want to do the the following operation in the Node parameters:

 {"frame_prefix": LaunchConfiguration("namespace") + "/"}

detailed Node:

robot_state_publisher_node = Node(
    package="robot_state_publisher",
    executable="robot_state_publisher",
    output='screen',
    namespace=LaunchConfiguration('namespace'),
    parameters=[
        {"robot_description": Command(["xacro ", LaunchConfiguration("xacro_file")])},
        {"publish_frequency": 60.0},
        {"use_tf_static": False},
        {"ignore_timestamp": True},
        {'use_sim_time': LaunchConfiguration("use_sim_time")},
        # {"frame_prefix": LaunchConfiguration("namespace"). + "/"}
    ], )

Is there anything to do with perform member function of LaunchConfiguration?