如何打印出列表中的总元素。 我需要一个函数，将打印出在val_holder列表中的总元素，它应该放在代码中的什么地方，如果我能得到完整的代码实现，我将不胜感激

import kivy
from kivy.app import App
from kivy.uix.floatlayout import Floatlayout
from kivy.uix.widget import Widget
from kivy.uix.button import Button
from kivy.label import Label 

val_holder=[]

class LandingScreen(FloatLayout):
    def __init__(self, **kwargs):
        super(LandingScreen, self).__init__(**kwargs)

  # put whatever pos_hint value you want.          
self.btn1=Button(text='button1 ', size_hint=(0.5, 0.5), on_press=self.click_b1))
self.btn2=Button(text='button1 ', size_hint=(0.5, 0.5), on_press=self.click_b2))
self.btn3=Button(text='button1 ', size_hint=(0.5, 0.5), on_press=self.click_b3))


            
self.add_widget(self.btn1)
self.add_widget(self.btn2)
self.add_widget(self.btn3)

     def click_b1(self, instance):
          val_holder.append('a') 
     def click_b2(self, instance):
          val_holder.append('b')
     def click_b3(self, instance):
          val_holder.append('c') 

 # I need a function to print out the total element in the val_holder list     

class SplashApp(App):
    def build(self):
        return LandingScreen()

if __name__ == '__main__':
    SplashApp().run()