Python tkinter StringVar trace method to moniter the read , write or deleted status

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For an StringVar() so we can check the different modes of this variable, like this

r :Read - the variable is read by someone
w :Write- the variable is written by someone.
u :undefined – The variable is deleted

Here is an example which uses w ( write ) mode to display the value of the variable when ever it changes.
We used one Button and used on Click event to change the value of this variable str from Hello to Welcome.

b1 = tk.Button(my_w,text='Update'command=lambda:str.set('Welcome') )

This triggers the trace() which used the callback function my_r() to print the value of the variable ( Welcome ) to our console.

trace method is used to attach 'observer' callbacks to the variable

import tkinter as tk
my_w = tk.Tk()
my_w.geometry("300x200")  # Size of the window 
my_w.title("www.plus2net.com")  # Adding a title

def my_r(*args):
    print(str.get()) #  Print when variable changes.
	
str = tk.StringVar(my_w) # declare StringVar()
str.set('Hello') 

l3 = tk.Label(my_w,  textvariable=str, width=15 )  
l3.grid(row=2,column=1)

b1 = tk.Button(my_w,text='Update',command=lambda:str.set('Welcome'))  
b1.grid(row=2,column=3)

str.trace('w',my_r)

my_w.mainloop()

Output

Welcome

Python Tkinter Dictionary Python- Tutorials

	22-03-2021
Very bad to call a variable in Python "str" str = tk.StringVar(my_w) # declare StringVar() because str is build-in method to stringify data! class str(object='') --> built-in function in Python

	23-03-2021
Thanks, Let us use str1

Python tkinter StringVar() trace