from tkinter import *
import random
st = [i+1 for i in range(1000)]
def printer(event):
    number = random.choice(st)
    lab.config(text = number)
root=Tk()
lab = Label(root, text = 0)
but=Button(root)
but["text"] = "Start"
but.bind("<Button-1>",printer)
lab.pack()
but.pack()
root.mainloop()