Use value of LaunchConfiguration in ROS2 launch file like a variable

edit

I found a way to do it :D Here is an example:

from launch import LaunchDescription, LaunchContext
from launch.actions import OpaqueFunction
from launch.substitutions import LaunchConfiguration
from launch_ros.actions import Node

def example_func(context: LaunchContext, arg1: LaunchConfiguration):
    value = context.perform_substitution(namespace)
    value +="/miracle/" # you can use it as a python variable now :D
    return Node(name=value)

def generate_launch_description():
    name = LaunchConfiguration('name')
    return LaunchDescription([
        OpaqueFunction(function=example_func, args=[namespace])
    ])

Normally, ROS2 will first build the context and afterwards execute everything, so it is not possible to get any value. With the OpaqueFunction() one can delay the execution of code, so that the context exists and the value can be retrieved. (See documentation)

I hope this example is understandable and can help someone.