U2 - Graficacion de un Circulo

from Tkinter import *

def poligono(val1, val2,val3,val4):
    v1 = Toplevel(ventana)
    v1.title('Grafica')
    v1.protocol('WM_DELETE_WINDOW', 'onexit')
    v1.geometry('500x500')
    grafica = Canvas(v1, width = 300 , height = 300, bg = 'black')
    grafica.pack(expand=YES, fill=BOTH)
    val1= int(e1.get())
    val2= int(e2.get())
    val3 = int(e3.get())
    val4 = int(e4.get())
    grafica.create_oval(val1, val2, val3, val4, fill = 'red')
    b = Button(grafica, text = 'Regresar', command = lambda: ejecutar(ocultar(v1)))
    b.grid(row = 1, column = 3)





def ocultar(v1):