from tkinter import *

a=Tk()

a.geometry('300x300')

x=0

y=True

z=1

def f():

global y

y=True

a.after(200,ks)

def ks():

global x,y,z

if 0<=x<270:

if y==True:

if z==1:

x+=10

L4.place(x=x,y=20)

elif z==0:

x-=10

L4.place(x=x,y=20)

a.after(200,ks)

else:

x=x

elif x>=270:

z=0

x-=10

L4.place(x=x,y=20)

a.after(200,ks)

elif x<0:

z=1

x=x+10

L4.place(x=x,y=20)

a.after(200,ks)

def tz():

global y

y=False

a.after(200,ks)

L4=Label(a,text='你好！',font=('黑体',16))

L4.place(x=x,y=20)

b1=Button(a,text='开始',command=f)

b1.place(x=100,y=50)

b2=Button(a,text='停止',command=tz)

b2.place(x=200,y=50)