Tkinter Entry size limit

[menator01]

You could test the length of the input and throw an error and remind that only 5 characters are allowed.

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Quick example

import tkinter as tk
from tkinter import messagebox

def callback(field, arg):
    arg = arg.get()
    if len(arg) != 5:
        messagebox.showerror('Error', 'field must contain 5 characters')
        field.delete(0, tk.END)
    else:
        messagebox.showinfo('Correct', 'This field has 5 characters')

root = tk.Tk()
var = tk.StringVar()
contain = tk.LabelFrame(root, text='Some label text')
contain.pack(fill='both', expand=True)

field = tk.Entry(contain, textvariable=var, bd=2)
field.pack(fill='x', expand=True)

btn = tk.Button(contain, text='Submit', command=lambda: callback(field, var))
btn.pack(side='left', fill='x', pady=5)

root.mainloop()