how do I make a ros publisher run under python 3?

edit

I made a python3 script that will read left, right encoder ticks from an arduino. I am trying to now get that same code to publish those ticks. This is what I have so far. sorry I not at all good with python.

    #!/usr/bin/env python3
import serial
import time
import rospy
from std_msgs.msg import Int16
# assign your port and speed
ser = serial.Serial('/dev/ttyUSB0', 1152000)
print("Reset Arduino")
time.sleep(3)
while (1)  # WORKING PART
    #left encoder read
    ser.write(bytes('l', 'UTF-8'))
    left = ser.readline().decode('ascii').strip()
    print("left")
    #print(left)
        #right encoder read
    ser.write(bytes('r', 'UTF-8'))
    right = ser.readline().decode('ascii').strip()
    right = right.rstrip('\r\n')
    print('right')
    #print(right)
    time.sleep(.0125)
    #node to publish left to lwheel (std_msgs/Int16)
#not working part
    def leftticks():
        pub = rospy.Publisher('lwheel', Int16)
        rospy.init_node('leftticks')
        while not rospy.is_shutdown():
            lstr = left
            rospy.loginfo(lstr)
            pub.publish(String(lstr))
            rospy.sleep(.5)


    if __name__ == '__main__':
        try:
            leftticks()
        except rospy.ROSInterruptException:
            pass

    #node to pulish right to rwheel (std_msgs/Int16)
    def rightticks():
        pub = rospy.Publisher('rwheel', Int16)
        rospy.init_node('rightticks')
        while not rospy.is_shutdown():
            rstr = right
            rospy.loginfo(rstr)
            pub.publish(String(rstr))
            rospy.sleep(.5)


    if __name__ == '__main__':
        try:
            rightticks()
        except rospy.ROSInterruptException:
            pass

How do I get it all to work together. As you can tell I have no clue what I am doing. Thanks for any help you can give.