Переключение между полями и ограничение пользовательского ввода

import tkinter
from tkinter import*
 
root=Tk()
 
def retrieve_input():
    inputValue1=Edit1.get("1.0","end-1c")
    inputValue2=Edit2.get("1.0","end-1c")
    print(inputValue1+' || '+inputValue2)
 
Edit1=Text(root, width=1, height=1, font='TrebuchetMS 12 bold', fg='black')
Edit1.place(x=5, y=5)
Edit2=Text(root, width=1, height=1, font='TrebuchetMS 12 bold', fg='green')
Edit2.place(x=20, y=5)
Btn=Button(root, text='action', command=lambda: retrieve_input())
Btn.place(x=50, y=5)
 
root.mainloop()

import tkinter as tk  # python 3.x
# import Tkinter as tk # python 2.x
 
class Example(tk.Frame):
 
    def __init__(self, parent):
        tk.Frame.__init__(self, parent)
 
        # valid percent substitutions (from the Tk entry man page)
        # note: you only have to register the ones you need; this
        # example registers them all for illustrative purposes
        #
        # %d = Type of action (1=insert, 0=delete, -1 for others)
        # %i = index of char string to be inserted/deleted, or -1
        # %P = value of the entry if the edit is allowed
        # %s = value of entry prior to editing
        # %S = the text string being inserted or deleted, if any
        # %v = the type of validation that is currently set
        # %V = the type of validation that triggered the callback
        #      (key, focusin, focusout, forced)
        # %W = the tk name of the widget
 
        vcmd = (self.register(self.onValidate),
                '%d', '%i', '%P', '%s', '%S', '%v', '%V', '%W')
        self.entry = tk.Entry(self, validate="key", validatecommand=vcmd)
        self.text = tk.Text(self, height=10, width=40)
        self.entry.pack(side="top", fill="x")
        self.text.pack(side="bottom", fill="both", expand=True)
 
    def onValidate(self, d, i, P, s, S, v, V, W):
        self.text.delete("1.0", "end")
        self.text.insert("end","OnValidate:\n")
        self.text.insert("end","d='%s'\n" % d)
        self.text.insert("end","i='%s'\n" % i)
        self.text.insert("end","P='%s'\n" % P)
        self.text.insert("end","s='%s'\n" % s)
        self.text.insert("end","S='%s'\n" % S)
        self.text.insert("end","v='%s'\n" % v)
        self.text.insert("end","V='%s'\n" % V)
        self.text.insert("end","W='%s'\n" % W)
 
        # Disallow anything but lowercase letters
        if S == S.lower():
            return True
        else:
            self.bell()
            return False
 
if __name__ == "__main__":
    root = tk.Tk()
    Example(root).pack(fill="both", expand=True)
    root.mainloop()