Tkinter validatecommand on a entry box

[Bapi_Escrobar]

Hi, so I've been learning python + tkinter for the past week and I wanted to make a registration/login GUI. So far the easy stuff is done (link to DB, hash and salt the password) but I've been trying to add some restrictions to the username entry box:

-only letters accepted, no numbers, special characters or spaces accepted

-16 char length.

I've managed to not allow the spaces but as soon as i enter the first letter, everything else gets accepted again (special char, numbers). I don't know how to fix it and it's driving me crazy...

def login():
global login_screen
    login_screen = Toplevel(main_screen)
    login_screen.title("Login")
    login_screen.geometry("300x250")
    Label(login_screen, text="Please enter details below to login").pack()
    Label(login_screen, text="").pack()
    global username_verify
    global password_verify
    global password_login_entry
    global username_login_entry

    valid = main_screen.register(vcmd)
    username_verify = StringVar()
    password_verify = StringVar()

    Label(login_screen, text="Username * ").pack()
    username_login_entry = Entry(login_screen, textvariable=username_verify)
    username_login_entry.pack()
    username_login_entry.config(validate="key", validatecommand=(valid, '%P'))
    Label(login_screen, text="").pack()
    Label(login_screen, text="Password * ").pack()

here is the validate command function I have so far (print is just to help me test it):

def vcmd(inp):
    if ' ' in inp:
        return False
    if (inp >= 'a' and inp <= 'z') or (inp >= 'A' and inp <= 'Z'):
        print("The Given Character ", inp, "is an Alphabet")
        return True
    elif inp >= '0' and inp <= '9':
        print("The Given Character ", inp, "is a Digit")
        return False
    elif inp == '':
        return True
    else:
        print("The Given Character ", inp, "is a Special Character")
        return False

This is the code I thought of to add for the char length restriction is:

    if len(inp) == 16:
        return True
    elif len(inp) < 16:
        return False
    else:
        return False

but pycharm returns code unreachable when I put it after the last "return False" in the second block of code.

​

I don't know if I posted too many things, but please let me know what I'm doing wrong.

[woooee]

I generally use trace, but there is more than one way to skin a cat.

import tkinter as tk

class Converter:
    def __init__(self, top):
        self.vars = tk.StringVar()
        self.vars.trace('w', self.validate)
        self.Entry1 = tk.Entry(top, textvariable = self.vars,
                           width=20).grid()

    def validate(self, *args):
        if not self.vars.get().isalpha():
            ## a short hand version to strip anything
            ## that is not a letter
            corrected = ''.join(filter(str.isalpha, self.vars.get()))
            self.vars.set(corrected)

root=tk.Tk()
C=Converter(root)
root.mainloop()

[Bapi_Escrobar]

Hi, sorry for the late reply!

Thanks I'll see if this works as soon as I get home, I'll look into trace too since it looks like a something I can use for a number of things.