tkinter缺少按钮中的文本

Question

当我运行程序tkinter doet时，将文本放在按钮上

num=tk.Entry(width=10)
plus=tk.Button(self, text="plus", padx=39, pady=20, command=Plus)
minus=tk.Button(self,text="-",width=10,height=10,command=Minus)
multi=tk.Button(self,text="*",width=10,height=10,command=Multi)
divide=tk.Button(self,text="/",width=10,height=10,command=Divide)
equate=tk.Button(self,text="=",width=10,height=10,command=finish)

num.grid(row=0,column=0)
plus.grid(row=1,column=0)
minus.grid(row=1,column=1)
multi.grid(row=1,column=2)
divide.grid(row=1,column=3)
equate.grid(row=1,column=4)