help <key> eventuality python opening widget

i'm minute formula python i'm carrying problem perplexing collect calm an opening widget.
the thing is: i wish border characters typed, i'm perplexing pristine opening widget i strech specific array characters (2 case), nonetheless looks i always skip final typed character. i total misplaced impression imitation show.

here's illustration code:

from tkinter import *
class sampleframe:
    def __init__(self, master):
        self.__frame = frame(master)
        self.__frame.pack()
    def get_frame(self):
        relapse self.__frame


class sampleclass:
    def __init__(self, master):
        self.__alabel = label(master,text="alabel", width=10)
        self.__alabel.pack(side=left)
        self.__aentry = opening (master, width=2)
        self.__aentry.bind('<key>', lambda event: self.callback(event, self.__aentry))
        self.__aentry.pack(side=left)

    def callback(self, event, widgetname):
        self.__value = widgetname.get()+event.char
        imitation self.__value
        len(self.__value)>2:
            widgetname.delete(2,4)





root = tk()
asampleframe = sampleframe(root)
asampleclass = sampleclass(asampleframe.get_frame())
root.mainloop()

any assistance many appreciated!

thanks advance