Can't understand how to validate entry widget in tkinter

Question

I am trying to interactively validate an entry widget in tkinter to only allow the user to enter characters in the alphabet. I have already read a very popular thread (Interactively validating Entry widget content in tkinter) and from that I have tried to figure out my solution but I just cannot seem to get it working. In the comments of that thread was a solution that only allowed numbers, I have used that for one area of my program and it works perfectly! Code here:

from tkinter import *

root = Tk()

def testVal(inStr,i,acttyp):
    ind=int(i)
    if acttyp == '1': #insert
        if not inStr[ind].isdigit():
            return False
    return True

entry = Entry(root, validate="key")
entry['validatecommand'] = (entry.register(testVal),'%P','%i','%d')
entry.pack()

root.mainloop()

I would like a solution like this, with the only change being that it accepts letters instead of numbers. Any help appreciated

Answer 1

Here's the solution you're looking for:

def testVal(inStr,i,acttyp):
    ind=int(i)
    if acttyp == '1': #insert
        if not inStr[ind].isalpha():
            return False
    return True

Heres some other things which might be useful:

• .isdigit() tests if a string is an integer
• .isalpha() tests if a string contains only letters
• .isalnum() tests if a string contains only letters and numbers
• .isupper() tests for uppercase
• .islower() tests for lowercase

For other datatypes you can use isinstance(), for example isinstance("34.5", float) will return True

Source: https://docs.python.org/3/library/stdtypes.html