Erreur de code python

from tkinter import *
class sizegrid:
    def __init__(self):
        self.__root = root.Tk ()
        self.createwidgets()
    def createwidgets(self):
        
        self.__c1 = Checkbutton(self.__root, text = "grille 4X4", height = 2, width = 10)
        self.__c2 = Checkbutton(self.__root, text = "grille 5X5", height = 2, width = 10)
        self.__c3 = Checkbutton(self.__root, text = "grille 6X6", height = 2, width = 10)
        self.__c4 = Checkbutton(self.__root, text = "grille 7X7", height = 2, width = 10)
        self.__c5 = Checkbutton(self.__root, text = "grille 8X8", height = 2, width = 10)
        
        c1.pack()
        c2.pack()
        c3.pack()
        c4.pack()
        c5.pack()
        root.mainloop()