Python: serialHelper with rospy (threading conflict?)

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Hi,

here a little script which works fine until I remove the remark for init of the roc node

#!/usr/bin/env python

import threading
from time import sleep
import rospy

import serialHelper


sh = serialHelper.SerialHelper()
NODE_NAME ='SerialHelperTestRos'

if __name__ == '__main__':
    try:
        t = threading.Thread(target=sh.serialReader)
        t.setDaemon(True)
        t.start()
        h = 0
        #rospy.init_node(NODE_NAME, anonymous=True)
        while True:
            sh.writeToSerial('Hello Nr' + str(h))
            h = h + 1
            resp = sh.getResponse()
            print ('response ' + resp)
            sleep(3)
    except Exception as e:
        print (e)

it's on ubuntu mate with python 2.7. Any idea why I don't see serial input when rod did init ? I am new to python and ros so any input is greatly appreciated