from tkinter import *
def frame(root, side):
    w = Frame(root)
    w.pack(side=side, expand=YES, fill=BOTH)
    return w
def button(root, side, text, command=None):
    w = Button(root, text=text, command=command)
    w.pack(side=side, expand=YES, fill=BOTH)
    return w
class Calculator(Frame):
    def __init__(self):
        Frame.__init__(self)
        self.pack(expand=YES, fill=BOTH)
        self.master.title('Simple Calculator')
        self.master.iconname("calc1")
        display = StringVar()
        Entry(self, relief=SUNKEN,textvariable=display).pack(side=TOP,expand=YES, fill=BOTH)

        for key in ("123", "456", "789", "-0."):
            keyF = frame(self, TOP)
            for char in key:
                button(keyF, LEFT, char,
                 lambda w=display, s='%s'%char: w.set(w.get()+s))
        opsF = frame(self, TOP)
        for char in "+-*/=":
            if char == '=':
                btn = button(opsF, LEFT, char)
                btn.bind('<ButtonRelease-1>',
                    lambda e, s=self, w=display: s.calc(w), '+')
            else:
                btn = button(opsF, LEFT, char,
                    lambda w=display, c=char: w.set(w.get()+' '+c+' '))
        clearF = frame(self, BOTTOM)
        button(clearF, LEFT, 'Clr', lambda w=display: w.set(''))
    def calc(self, display):
        try:
            display.set(eval(display.get()))
        except ValueError:
            display.set("ERROR")
if __name__ == '__main__':
    Calculator().mainloop()