from Tkinter import *
def q(e):
 v=s.get()
 if v:s.delete(0,END);s.insert(0,eval(v))
t=Tk()
s=Entry(t)
s.grid(columnspan=4)
for i,o in enumerate(Button(t,text=o)for o in"789/456*123-0.=+"):o.bind("<1>",{"=":q}.get(o["text"],lambda e:s.insert("end",e.widget["text"])));o.grid(column=i%4,row=1+i/4)
t.mainloop()