tkinter NameError：名称“表达式”未定义

如何解决tkinter NameError：名称“表达式”未定义

我是这个Uno计算器的问题，我不得不将它嵌套在一个def中 但现在它不会显示方程式 只是不断得到 表达式=表达式+ str（num） NameError：名称“表达式”未定义

正常运行时效果很好

from tkinter import *
root = Tk()
def Run():
    expression = ""
    top3 = Tk() 
    top3.title("score Calqleter") 
    equation = StringVar() 
    expression_field = Entry(top3,textvariable=equation) 
    expression_field.grid(columnspan=4,ipadx=70) 
    equation.set('click the cards to add') 
      
    def press(num):
        global expression
        expression = expression + str(num) 
        equation.set(expression)
    def equalpress(): 
        try: 
            global expression 
            total = str(eval(expression[:-1])) 
            equation.set(total) 
            expression = "" 
        except: 
            equation.set(" error ") 
            expression = "" 
    def clear(): 
        global expression 
        expression = "" 
        equation.set("")  
    button1 = Button(top3,text=' Card1 ',fg='black',bg='red',command=lambda: [press(1),press("+")],height=7,width=7) 
    button1.grid(row=2,column=0) 
    button2 = Button(top3,text=' Card2 ',command=lambda: [press(2),width=7)  

run = Button(root,text = 'Enter Your Text',command = Run)
run.pack()

root.mainloop()