How to validate a Tkinter entry widget to only accept string?

Question

I am trying to work my way through Tkinter and this is a part of my code:

 FirstName = Label(canvas, text="First Name")
 FirstName.configure(width=30, bg="white", fg="black", border=10)
 FirstName = canvas.create_window(330, 130, anchor = CENTER, window=FirstName)

 FName_Entry = Entry(canvas)
 canvas.create_window(850, 145, window=FName_Entry, height=35, width=300)

As you can see this is an entry widget for users to enter their first name. how can I validate this to only accept string (letters) and if they try to enter integers, symbols or basically anything that is not a letter, it should display a message on the side of the widget urging users to enter a valid name.

I tried to check online but most of them are using classes and I am not used to classes as of yet and am new to Tkinter. other examples explain how to limit entry to integers so I am a bit confused here. Thanks for helping!

Answer 1

Here is a small snippet to actually make you understand better

from tkinter import * 
from tkinter import messagebox

root = Tk()

def check():
    sel = e.get()
    
    if not sel.isalpha():
        messagebox.showerror('Only letters','Only letters are allowed!')

e = Entry(root)
e.pack(pady=10)

b = Button(root,text='Click Me',command=check)
b.pack(padx=10,pady=10)

root.mainloop()

Here we are checking if sel.isalpha() returns False or not, if it does, then show a messagebox saying only letters are allowed. Simple as that.

Do let me know if any errors. Happy coding

Here is more on isalpha() method

Cheers

Answer 2

You can use list in which you can store the letter which is to be accepted. Then check the each letter of the input with the element in the list. If any character not found from the input in the list(acceptable character) then it is invalid input.

# acceptable character list
accepted_characters = ['a', 'b', 'c',.....'z', 'A', 'B', 'C',...'Z']

# input from the tkinter entry widget
inp = "hello"

for i in inp:
    if i not in accepted_characters:
        print('Invalid data.')

Another way is using RegEx module which is built-in module. But I am not too familiar with RegEx.