hx711 python library; ROS node; name 'rospy' is not defined

edit

hi
for running python scrip you must use "rosrun" ,somting lik this:

rosrun pkg_name py_test.py

also pls see the wiki

i have the same problem to with arduino and ros commmunication.when i use hx711 library and ros library together i get this msg."Unable to sync with device; possible link problem or link software version mismatch such as hydro rosserial_python with groovy Arduino"

this is my code on arduino

#include <ros.h>
#include <std_msgs/Float64.h>
#include "HX711.h"
#define DOUT  3//
#define CLK  2//
HX711 scale;
float calibration_factor = -5880; //-7050 worked for my 440lb max scale setup
ros::NodeHandle nh;

std_msgs::Float64 test;
ros::Publisher p2("my_topic", &test);
void setup()
{ 
  delay(2000);
  scale.begin(DOUT, CLK);
  scale.set_scale();
  scale.tare(); //Reset the scale to 0 
  long zero_factor = scale.read_average(); //Get a baseline reading
  delay(2000);
  nh.initNode();
  nh.advertise(p2);
  delay(2000);
}

void loop()
{
  delay(200);
  scale.set_scale(calibration_factor); //Adjust to this calibration factor
  float weight=(scale.get_units());
  test.data = weight;
  p2.publish( &test );
  nh.spinOnce();
}

ros command is this

rosrun rosserial_python serial_node.py /dev/ttyUSB1

is there any way to use hx711 withouth library.