# Inspired by code from Jesse Weinstein
import Tkinter as tk

def onOtherButton(event):
    screen.insert("end", event.widget["text"])

def onBackspace(event):
    screen.delete( len(screen.get())-1 )

def onEquals(event):
    screen_get = screen.get()
    if screen_get:
        screen.delete(0, "end")
        screen.insert(0, eval(screen_get) )

root = tk.Tk()
screen = tk.Entry(root)
screen.grid(columnspan=4, pady=4)

specialBut = {"c":onBackspace, "=":onEquals}
buttons = [tk.Button(root, text=op, width=3) for op in "789/456*123-0c=+"]
for pos,oper in enumerate(buttons):
    oper.bind("<1>", specialBut.get(oper["text"], onOtherButton))
    oper.grid(column=pos%4, row=1+pos/4, pady=4)

root.mainloop()