go.py

import tkinter as tk
from xml.dom import minidom
import threading
from time import sleep

dist = 0.0

class parse_xml(threading.Thread):
    global dist
    def run(self):
        while(True):
            try:
                xmldoc = minidom.parse('data.xml')
                itemlist = xmldoc.getElementsByTagName('object1')
                for items in itemlist:
                    x = items.getElementsByTagName('x1')[0].childNodes[0].data

                x_per_inch = (.7129988670349121-.28)/28
                xml_distance = float(x)

                if float(xml_distance) <= .28:
                    dist = 0.0
                    print("STOP")
                else:  
                    dist = ((xml_distance-.28)//x_per_inch)
            # if we get caught in a write loop, keep old data        
            except Exception as e:
                return

class Gui(object):
    global dist
    def __init__(self):
        self.root = tk.Tk()
        self.lbl = tk.Label(self.root, text="")
        #self.lbl = Lab
        self.updateGUI()

    def run(self):
        self.lbl.pack()
        self.lbl.after(1000, self.updateGUI)
        self.root.mainloop()

    def updateGUI(self):
        msg = str(dist)
        self.lbl["text"] = msg
        self.root.update()
        self.lbl.after(1000, self.updateGUI)

if __name__ == "__main__":
    parse_xml().start()
    Gui().run()