Python: python的简单表达式计算器

这是一个简单的表达式计算器, 不太懂用Tkinter写GUI, 参考了别人的代码
from __future__ import division
from Tkinter import Tk, Entry, Button, Label, mainloop
from tkFont import Font
def get_value ():
v = ''
try:
v = eval(text.get()) #use eval to calculate the vlaue of the text
except:
pass
if isinstance(v, (int, float, long)):
pass
else:
v = 'Error...'
label.config(text = v) #use config to change the text


top = Tk()
top.title("calculator")
ft = Font(family = 'Courier New', size = 12)
text = Entry(top, font = ft)
button = Button(top, text = 'Ok', command = get_value)
label = Label(text = '(+ - * / % **)', font = ft)
Enter = lambda x: x.keycode == 13 and get_value()
Key = lambda x: label.config(text = '(+ - * / % **)')
text.bind('<Key>', Enter) #when the key is enter, execute the function Enter
text.focus()
text.bind('<Button-1>', Key) #when click the left-key, execute the function Key
text.pack()
button.pack()
label.pack()
mainloop()