Zoom in on Python's picture

from tkinter import *

from tkinter.filedialog import *

from tkinter.simpledialog import*

def func_open() :

filename = askopenfilename (parent = window, files = ("GIF files", "*.gif"), ("all files", "*.*"))
photo = PhotoImage(file = filename)
pLabel.configure(image = photo)
pLabel.image = photo

def func_exit() :

window.quit()
window.destroy()

def func_zoom() :

value = askinteger ("Enlarge multiple", enter a multiple to enlarge (2-8), minvalue = 2, maxvalue = 6)
global photo
photo = photo.zoom(value,value) #zoom

def func_subsample() :

value = askinteger ("reduce multiple", enter a multiple to reduce (2-8), minvalue = 2, maxvalue = 6)
global photo
photo = photo.subsample(value,value) #reduce

window = Tk()

window.geometry("400x400") window.title<:/p>

photo = PhotoImage() pLabel = Label(window, image = photo)

pLabel.pack(expand=1, anchor = CENTER)

mainMenu = Menu(window)

window.config(menu = mainMenu)

fileMenu = Menu(mainMenu)

mainMenu.add_cascade(label = "file", menu = fileMenu)

fileMenu.add_command(label = "Open File", command = func_open)

fileMenu.add_separator()

fileMenu.add_command(label = "End Program", command = func_exit)

fileMenu = Menu(mainMenu) #Create a new parent menu

mainMenu.add_cascade(label="image effect", menu=filMenu) #TopMenuName

fileMenu.add_command(label="zoom", command=func_zoom) #create submenu

FileMenu.add_separator() #Generate lines between submenus

fileMenu.add_command(label = "reduce", command = func_subsample) #create submenu

window.mainloop()

Select a file, press the upper menu image effect, press Zoom or Zoom to display the message box, and then enter a number in the message box, but you can't zoom in or out after that Could you tell me which part is wrong?