python tkinter listbox 添加Scrollbar 滚动条

#创建listbox        
user_listbox=tk.Listbox(root,font=('',14))        

user_listbox.place(x=5,y=100,relwidth=0.9,relheight=0.9)

#创建Scrollbar
yscrollbar = tk.Scrollbar(user_listbox,command=user_listbox.yview)
yscrollbar.pack(side=tk.RIGHT, fill=tk.Y)
user_listbox.config(yscrollcommand=yscrollbar.set)