python Traceback about tkinter that I can't fix :     from tkinter import *
    window_main = Tk()

    def window_open():
	    def chgColor(event):
	    lst["bg"] = lst.get(lst.curselection())

	    window_public = Tk()
	    window_public.title("New Page")
	    lbl = Label(window_public, text = "Today is a good day and I'm a gooie!")
	    lbl.grid(padx = 20, pady = 10)
	    var = StringVar()
	    lst = Listbox(window_public, height = 5, width = 10, listvariable = var)
	    lst.grid(padx = 50, pady = 20)
	    list = ["red", "blue", "yellow", "pink", "green", "white", "black"]
	    var.set(tuple(list))
	    lst.bind("<<ListboxSelect>>", chgColor)
	    window_public.mainloop()


    window_main.title("Main")
    window_main_btn = Button(window_main, text = "To New Page", command = window_open)
    window_main_btn.grid(padx = 50, pady = 20)
    window_main.mainloop()




I'm a beginner of  python and  get stuck in this problem for several days. When I click on the button and get in new page then click on listbox I'll get a traceback.  I still can't understand what the traceback's meaning and can't fix it. But I found when I delete codes about window_main, it could run. I need your help!!

