Python - 三级菜单优化方法 (单层循环)

 menu = {
......
 }
 current_layer = menu
 layers = []
 while True:
     for k in current_layer:
         print(k)
     choice = input('>:').strip()
     if not choice:continue
     if choice in current_layer:
         layers.append(current_layer)
         current_layer = current_layer[choice]
     elif choice == 'q':
         break
     elif choice == 'b':
         if len(layers) != 0:
             current_layer = layers.pop()
         else:
             print('-------Top!-------')