Tkinter Smallest Calculator ever

This is the smallest calculator you can get… with tkinter module to make a grafic user interface (very minimal, indeed).

from tkinter import *

# This class inherit from Frame
class App(Frame):
    def __init__(self):
        Frame.__init__(self)
        self.option_add("*Font", "arial 20 bold")
        self.pack(expand=YES, fill=BOTH)
        self.master.title("Calculator")
        # the widgets: display, clear button...
        self._display()

    def _display(self):
        display = StringVar()
        entry = Entry(
            self,
            relief=FLAT,
            textvariable=display,
            justify='right',
            bd=15,
            bg='orange')
        entry.pack(side=TOP)
        entry.focus()
        self.master.bind("<Return>", lambda x: self.calc(display))
        self.master.bind("<Escape>", lambda x: display.set(""))


    def calc(self, display):
        try:
            ris = eval(display.get())
            if str(display.get()) == str(ris):
                display.set("")
            else:
                display.set(ris)
        except NameError as e:
            display.set("ERR: press ESC")


if __name__ == '__main__':
    App().mainloop()

This is what it looks like, and do not say I didn’t warned you