How to write proper launch file by passing arguments?

edit

I trying to write launch file. But i could not find proper solution anywhere.

Python code:

parser = argparse.ArgumentParser(description='Script to run MobileNet-SSD object detection network ')
parser.add_argument("--prototxt", default="/home/user/catkin_ws/src/human_ssd/model/MobileNetSSD_deploy.prototxt",
                                  help='Path to text network file: '
                                       'MobileNetSSD_deploy.prototxt for Caffe model or '
                                       )
parser.add_argument("--weights", default="/home/user/catkin_ws/src/human_ssd/model/MobileNetSSD_deploy.caffemodel",
                                 help='Path to weights: '
                                      'MobileNetSSD_deploy.caffemodel for Caffe model or '
                                      )
parser.add_argument("--thr", default=0.5, type=float, help="confidence threshold to filter out weak detections")
args = parser.parse_args(rospy.myargv()[1:])

Launch fie:

 <include file="$(find realsense2_camera)/launch/rs_camera.launch">
        <arg name="filters" default="temporal,spatial,hole_filling,decimation"/>
        <arg name="align_depth" default="true"/>
  </include>

  <arg name="--prototxt" default="$(find human_ssd)/model/MobileNetSSD_deploy.prototxt"/>
  <arg name="--thr"   default="0.3"/>
  <arg name="--weights" default="$(find human_ssd)/model/MobileNetSSD_deploy.caffemodel"/>

  <node pkg="human_ssd" type="detector.py" name="human_ssd_detector" output="screen">
        <param name="--prototxt" value="$(arg --prototxt)"/>
        <param name="--thr" value="$(arg --thr)"/>
        <param name="--weights" value="$(arg --weights)"/>
  </node>

So If i run command

roslaunch human_ssd detector.launch thr:=0.3

The thr takes the value of 0.5