param error (KeyError)

edit

Hi everyone! I started learn ROS. I try to read data from launch file with param. bu I give an error and I did not understand why? Please help me constructor:

def__init__(self,nodeName,goalx,goaly):
   rospy.init_node("node", anonymous="True")
   self.goalX = rospy.get_param("x1")
   self.goalY = rospy.get_param("y1")
   self.pub = rospy.Publisher(nodeName + '/cmd_vel',Twist,queue_size=10)
   self.sub = rospy.Subscriber(nodeName+"/odom",Odometry,callback=self.update_pose)
   self.odometry = Odometry()
   self.rate = rospy.Rate(10)
if __name__ == "__main__":
 nodeId = sys.argv[1]
try:
     nodeName = "robot_"+nodeId
     x = Turtlebot(nodeName,0,0)
     x.move2goal()
     rospy.spin()

Launch File:

    <param name="x1" type="int" value="4" />
<param name="y1" type="int" value="0" />
<param name="x2" type="int" value="5" />
<param name="y2" type="int" value="0" />


<node pkg="stage_ros" name="stageros" type="stageros" args="$(find beginner_tutorials)/world/worldfile.world" output="screen"/>



<!-- <node pkg="beginner_tutorials" name="rotate1" args="0"  type="projecttask2.py"/> -->
 <node pkg="beginner_tutorials" name="rotate2"  args="1" type="projecttask2.py">



</node>

Error: KeyError('x1')