UI demo

ui.py

from tkinter import Tk, Label, Button, StringVar

class AlprGui:
    def __init__(self, master):
        self.master = master
        master.title("Última placa patente reconocida")

        self.label_index = 0
        self.label_text = StringVar()
        self.label_text.set("")
        self.label = Label(master, textvariable=self.label_text)
        self.label.pack()

        self.close_button = Button(master, text="Close", command=master.quit)
        self.close_button.pack()

    def change_label(self, text):
        self.label_text.set(text)
        #si no anda lo anterior, entonces usar
        #self.label['text'] = text

root = Tk()
alpr_gui = AlprGui(root)
root.mainloop()

alpr_gui.change_label("HH-II-11")