python kivy APP 中 label 无法刷新问题

想做个APP试试
第二次按下按钮后，文本显示覆盖，并不会刷新

from cProfile import label
from cgitb import text
from lib2to3.pgen2.token import GREATER
import nntplib
from kivy.app import App
from kivy.uix.button import Button
from kivy.uix.floatlayout import FloatLayout
from kivy.uix.label import Label
from kivy.clock import Clock
import random
import string
global n
n=0
class ButtonFloatLayout(FloatLayout):
def init(self,**kwargs):
super(ButtonFloatLayout, self).init(**kwargs)

    bt=Button(text='click', background_color=[1,.5,.5,1],on_release=self.release_button, pos=(300,0),size_hint=(.2,.15))   #添加一个按钮
    bt.bind(on_press=self.press_button)   #绑定触发事件
    self.add_widget(bt)             #添加到布局
    
    

def press_button(self,arg):
    #x=10+n
    #self.ar = Label(text = '')
    #self.add_widget(self.ar)
    self.name_label = Label(text = '')
    self.add_widget(self.name_label)
    print('1')
    #print(x)
    

def release_button(self,arg):
    x=[]
    r=n+10
    for i in range(1,34):
        x.append(i)
    x2=random.sample(x,6)
    x2.sort()
    print(x2) 
    AF=x2   
    self.name_label = Label(text = str(AF))
    self.add_widget(self.name_label)
    print('2')
    

class ButtonApp(App):
def build(self):
return ButtonFloatLayout()

if name =='main':
ButtonApp().run()

我想要达到的结果
按下按钮后能刷新前一个显示的数据