Restricting the value in Tkinter Entry widget

Question

I need to restrict the values in the Entry widget to numbers only. The way I implemented is:

import numpy as np
from Tkinter import *;
import tkMessageBox;

         


        

Answer 1

I realize this is quite late for an answer but feel that I can give a lot simpler answer to this... it is really quite simple once you understand how it works.

Use the validating feature that comes with the Entry widget.

Lets assume self is a widget:

vcmd = (self.register(self.callback))

w = Entry(self, validate='all', validatecommand=(vcmd, '%P')) 
w.pack()

def callback(self, P):
    if str.isdigit(P) or P == "":
        return True
    else:
        return False

You don't need to include all of the substitution codes: ('%d', '%i', '%P', '%s', '%S', '%v', '%V', '%W'), only the ones you'll use are necessary.

The Entry widget returns a string so you will have to somehow extract any digits in order to separate them from other characters. The easiest way to do this is to use str.isdigit(). This is a handy little tool built right into python's libraries and needs no extra importing and it will identify any numerics (digits) that it finds from the string that the Entry widget returns.

The or P == "" part of the if statement allows you to delete your entire entry, without it, you would not be able to delete the last (1st in entry box) digit due to '%P' returning an empty value and causing your callback to return False. I won't go into detail why here.

validate='all' allows the callback to evaluate the value of P as you focusin, focusout or on any key stroke changing the contents in the widget and therefore you don't leave any holes for stray characters to be mistakenly entered.

In all, to make things simple. If your callback returns True it will allow data to be entered. If the callback returns 'False` it will essentially 'ignore' keyboard input.

Check out these two references. They explain what each substitution code means and how to implement them.

http://infohost.nmt.edu/tcc/help/pubs/tkinter/web/entry-validation.html http://stupidpythonideas.blogspot.ca/2013/12/tkinter-validation.html

EDIT: This will only take care of what is allowed in the box. You can, however, inside the callback, add whatever value P has to any variable you wish.

Answer 2

I had to deal with an initial insert case as well. This is what I have ended up with:

    def _checkNumberOnly(self, action, value_if_allowed):
        if action != '1':
           return True
        try:
            return value_if_allowed.isnumeric()
        except ValueError:
           return False

    vcmd = (self.register(self._checkNumberOnly), '%d', '%P')
        self.port = ttk.Entry(self, width=35, validate='key', validatecommand=vcmd)

Therefore it validates for the following:

    self.port.insert(0, '6379')

I'm not sure that the catch is needed, due to isnumeric() not stating it raises an exception.

Answer 3

The answer is almost perfect, just a little addition to allow for deleting the whole string. The check for floats should be done only when inserting text

def validate_float(self, action, index, value_if_allowed,
    prior_value, text, validation_type, trigger_type, widget_name):
    # action=1 -> insert
    if(action=='1'):
        if text in '0123456789.-+':
            try:
                float(value_if_allowed)
                return True
            except ValueError:
                return False
        else:
            return False
    else:
        return True

Answer 4

if you are dealing with locales that have a comma as decimal point:

locale.setlocale(locale.LC_ALL,'de_DE.UTF-8') # German

---

vcmd = (self.root.register(self.entry_numericonly), '%d', '%P')

---

self.my_float_entry = tk.Entry(self.root, ... , validate='key', validatecommand=vcmd)

---

def entry_numericonly(self, action, value_if_allowed):
    if(action == "1"):
        try:
            loc_float  = locale.atof(value_if_allowed)
            loc_float_format = locale.format("%f", loc_float)
            try:
                loc_same_length = loc_float_format[:len(value_if_allowed)]
                return value_if_allowed == loc_same_length
            except:
                return False                    
        except:
            return False
    else:
        return True

Answer 5

I'm new to python and Tkinker, but this works best for me:

    def keybind1 (self,event):
        v = event.char
        try:
            v = int(v)
        except ValueError:
            if v!="\x08" and v!="":
                return "break"

The v = int(v) triggers a ValueError on any key other then number keys, but the if v!="\x08 and v!="":" statement still allows the backspace, ("\x08"), and delete, arrow, home, end, etc. keys, (which have an event.char of ""), to work normally - otherwise the break command stops the entry of other characters into the Entry widget.

Answer 6

This uses validatecommand to restrict valid user input in the tk.Entry to strings which can be interpreted as floats:

import tkinter as tk

class window2:
    def __init__(self, master1):
        self.panel2 = tk.Frame(master1)
        self.panel2.grid()
        self.button2 = tk.Button(self.panel2, text = "Quit", command = self.panel2.quit)
        self.button2.grid()
        vcmd = (master1.register(self.validate),
                '%d', '%i', '%P', '%s', '%S', '%v', '%V', '%W')
        self.text1 = tk.Entry(self.panel2, validate = 'key', validatecommand = vcmd)
        self.text1.grid()
        self.text1.focus()

    def validate(self, action, index, value_if_allowed,
                       prior_value, text, validation_type, trigger_type, widget_name):
        if value_if_allowed:
            try:
                float(value_if_allowed)
                return True
            except ValueError:
                return False
        else:
            return False

root1 = tk.Tk()
window2(root1)
root1.mainloop()

References:

• The Tk man page explains the validate and validatecommand options. (Thanks to schlenk for the link).
• I learned how to do this in Python here.