Entry accept only float 8,2

Question

I have the need with tkinter python, to define an entry field that only accepts a float field with 8 integers and 2 decimals, perhaps with an error message if it does not respect the format 8.2. You can help me define a format for this field.

Answer 1

Entry has options validate= and validatecommand= which you can see in Interactively validating Entry widget content in tkinter

There is also A Validating Entry Widget

But you can also bind event <KeyRelease> to execute function which you can use to check value in Entry.

I split text using dot. If I get more then 2 parts then there was more then 2 dots.

After that I check second part if it exists, is not empty, has only digits and is not longer than 8 chars. Similar way I check first part.

When string is not valid then I only print message in console but you could do something more - you can display messagebox or replace text in Entry.

import tkinter as tk

def check(event):
    text = event.widget.get()
    print('text:', text)

    parts = text.split('.')
    parts_number = len(parts)

    if parts_number > 2:
        print('too much dots')

    if parts_number > 1 and parts[1]: # don't check empty string
        if not parts[1].isdecimal() or len(parts[1]) > 2:
            print('wrong second part')

    if parts_number > 0 and parts[0]: # don't check empty string
        if not parts[0].isdecimal() or len(parts[0]) > 8:
            print('wrong first part')

root = tk.Tk()

e = tk.Entry(root)
e.pack()
e.bind('<KeyRelease>', check)

root.mainloop()

---

EDIT: example with validate= - based on example from second link above.

Function check() mostly without changes. It only uses return True/False instead of printing messages. It blocks invalid values.

import tkinter as tk

def check(d, i, P, s, S, v, V, W):
    #print("d='%s'" % d)
    #print("i='%s'" % i)
    #print("P='%s'" % P)
    #print("s='%s'" % s)
    #print("S='%s'" % S)
    #print("v='%s'" % v)
    #print("V='%s'" % V)
    #print("W='%s'" % W)    

    text = P  #e.get()
    print('text:', text)

    parts = text.split('.')
    parts_number = len(parts)

    if parts_number > 2:
        #print('too much dots')
        return False

    if parts_number > 1 and parts[1]: # don't check empty string
        if not parts[1].isdecimal() or len(parts[1]) > 2:
            #print('wrong second part')
            return False

    if parts_number > 0 and parts[0]: # don't check empty string
        if not parts[0].isdecimal() or len(parts[0]) > 8:
            #print('wrong first part')
            return False

    return True

# --- main ---

root = tk.Tk()

vcmd = (root.register(check), '%d', '%i', '%P', '%s', '%S', '%v', '%V', '%W')

e = tk.Entry(root, validate='key', validatecommand=vcmd)
e.pack()

root.mainloop()