rclpy: Accessing ros2 launch args from main function

edit

I have a node in a package that I set up using ros2 pkg create --build-type ament_python --node-name my_node my_package

my_node.py looks like this:

import rclpy
from rclpy.node import Node

class MyNode(Node):
    def __init__(self, arg):
        super().__init__("my_node")
        self.arg = arg

def main(args = None):

    rclpy.init(args = args)

    node = MyNode(9)
    node.get_logger().info("Hello from my_node")

    try:
        rclpy.spin(node)
    except:
        pass

    node.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()

And my launch file looks like this:

from launch import LaunchDescription from launch_ros.actions import Node import launch

def generate_launch_description():
    return LaunchDescription([

        Node(
            package='my_package',
            node_namespace='test',
            node_executable='my_node',
            emulate_tty=True,
            node_name='my_node',
        ),
        launch.actions.DeclareLaunchArgument('arg1')
])

I am launching the node using ros2 launch -a ./launch/my_launch.py arg1:=9

How do I access arg1 from inside the main function? I want to use it to pass into the constructor of the Node.

Alternatively, is there another way to pass parameters into the main function? I just want to populate the args in the def main(args = None) function, but it needs to work when launched from a launch file.

Thanks