Не работает код на питоне:

from tkinter import *

bomb = 100
score = 0
best_score = 0
press_return = True


def start(event):
    global press_return
    global bomb
    global score
    if not press_return:
        pass
    else:
        bomb = 100
        score = 0
        label.config(text='')
        update_bomb()
        update_score()
        update_display()
        press_return = False


def update_display():
    global bomb
    global score
    if bomb > 50:
        bomb_label.config(image=normal_photo)
    elif 0 < bomb <= 50:
        bomb_label.config(image=no_photo)
    else:
        bomb_label.config(image=bang_photo)
    fuse_label.config(text='Fuse: ' + str(bomb))
    score_label.config(text='Score: ' + str(score))
    fuse_label.after(100, update_display)


def update_bomb():
    global bomb
    bomb -= 5
    if is_alive():
        fuse_label.after(400, update_bomb)


def update_score():
    global score
    score += 1
    if is_alive():
        score_label.after(3000, update_score)

def update_best_score():
    global best_score
    best_score += 1
    if is_alive():
        best_score_label.after(3000, update_best_score)


def click():
    global bomb
    if is_alive():
        bomb += 1


def is_alive():
    global bomb
    global press_return
    if bomb <= 0:
        label.config(text='Ban! Ban! Ban')
        press_return = True
        return False
    else:
        return True


root = Tk()
root.title('Ban Ban')
root.geometry('500x550')

label = Label(root, text='Press [enter] to start the game', font=('Georgia', 4))
label.pack()

fuse_label = Label(root, text='Fuse: ' + str(bomb), font=('Georgia', 6))
fuse_label.pack()

score_label = Label(root, text='Score: ' + str(score), font=('Georgia', 6))
score_label.pack()

best_score_label = Label(root, text='Best Score:' + str(best_score), font=('Georgia',6))
best_score_label.pack()

if best_score < score:
    best_score = score

no_photo = PhotoImage(file='img/bomb_no.png')
normal_photo = PhotoImage(file='img/bomb_normal.png')
bang_photo = PhotoImage(file='img/pow.png')

bomb_label = Label(root, image=normal_photo)
bomb_label.pack()

click_button = Button(root, text='Click me', bg='#000000', fg='#ffffff', width=15,
                    font=('Georgia', 6), command=click)
click_button.pack()

root.bind('<Return>', start)

root.mainloop()