Tkinter Entry size limit

[deanhystad]

You can use a validation callback to limit what is typed in an entry.

import tkinter as tk
from tkinter import messagebox

class Window(tk.Tk):
    def __init__(self):
        super().__init__()

        label = tk.Label(self, text="Zip Code")
        reg = self.register(self.zip_validate)
        self.zip_code = tk.StringVar(self, '')
        entry = tk.Entry(
            self,
            textvariable=self.zip_code,
            width=7,
            justify=tk.RIGHT,
            validate='key',
            validatecommand=(reg, '%P'))
        button = tk.Button(self, text='Accept', command=self.submit)

        button.pack(side=tk.BOTTOM, padx=5, pady=5, expand=True, fill=tk.X)
        label.pack(side=tk.LEFT, padx=5, pady=5)
        entry.pack(side=tk.RIGHT, padx=5, pady=5)

    @staticmethod
    def zip_validate(zip_code):
        return zip_code.isdigit() and len(zip_code) <= 5

    def submit(self):
        if len(self.zip_code.get()) < 5:
            messagebox.showerror('Error', 'Zip code must be 5 digits', parent=self)


Window().mainloop()

This example registers a validation callback function named 'zip_validate'. The function is called whenever a key is pressed ('key'). The function is passed a preview of what the entry contents will be if the key press is accepted ('%P'). The validator returns True if the new content is acceptable, else False.

Note that the validate function does not force the zip code to be 5 digits long. '123' is valid. To ensure that the zip code is 5 digits long you would still need some type of form validation very much like in menator's post.

In this example the validate function is a static method, but it can be a standalone function.

Read about validators here:

https://anzeljg.github.io/rin2/book2/240...ation.html
https://www.geeksforgeeks.org/python-tki...ry-widget/