Tkinter - Entry box - formatted for date

Thanks to @Bryan Oakley's major hint, I have come up with this working code.

(Update: threw a few years of programming experience and some recent readers' sharp eyes at improving the code.)

from __future__ import print_functiontry:    import Tkinter as tkexcept ImportError:    import tkinter as tkclass DateEntry(tk.Frame):    def __init__(self, master, frame_look={}, **look):        args = dict(relief=tk.SUNKEN, border=1)        args.update(frame_look)        tk.Frame.__init__(self, master, **args)        args = {'relief': tk.FLAT}        args.update(look)        self.entry_1 = tk.Entry(self, width=2, **args)        self.label_1 = tk.Label(self, text='/', **args)        self.entry_2 = tk.Entry(self, width=2, **args)        self.label_2 = tk.Label(self, text='/', **args)        self.entry_3 = tk.Entry(self, width=4, **args)        self.entry_1.pack(side=tk.LEFT)        self.label_1.pack(side=tk.LEFT)        self.entry_2.pack(side=tk.LEFT)        self.label_2.pack(side=tk.LEFT)        self.entry_3.pack(side=tk.LEFT)        self.entries = [self.entry_1, self.entry_2, self.entry_3]        self.entry_1.bind('<KeyRelease>', lambda e: self._check(0, 2))        self.entry_2.bind('<KeyRelease>', lambda e: self._check(1, 2))        self.entry_3.bind('<KeyRelease>', lambda e: self._check(2, 4))    def _backspace(self, entry):        cont = entry.get()        entry.delete(0, tk.END)        entry.insert(0, cont[:-1])    def _check(self, index, size):        entry = self.entries[index]        next_index = index + 1        next_entry = self.entries[next_index] if next_index < len(self.entries) else None        data = entry.get()        if len(data) > size or not data.isdigit():            self._backspace(entry)        if len(data) >= size and next_entry:            next_entry.focus()    def get(self):        return [e.get() for e in self.entries]if __name__ == '__main__':            win = tk.Tk()    win.title('DateEntry demo')    dentry = DateEntry(win, font=('Helvetica', 40, tk.NORMAL), border=0)    dentry.pack()    win.bind('<Return>', lambda e: print(dentry.get()))    win.mainloop()

I have discovered a very simple solution. I hope someone can find it useful.

self.entry1=tk.Entry(self)self.entry1.insert(END, "    /    /        ")self.entry1.config(fg="grey")def datemask(self, event):if len(self.entry1.get()) is 2:    self.entry1.insert(END,"/")elif len(self.entry1.get()) is 5:    self.entry1.insert(END,"/")elif len(self.entry1.get()) is 11:    self.entry1.delete(10, END)

Bind the entry widget

self.entry1.bind('<KeyRelease>', self.datemask)