Tkinter Radiobutton executes a command while already selected

In my Tkinter app, I want to execute on_choice function when selecting Radiobutton by using command=on_choice. When pressing on a radiobutton when it's already selected, the function should not be executed again. It should only be executed once after switching from another radiobutton, so the user could not repeatedly execute a function by pressing on the same radiobutton. Is there a way to prevent an execution of a command when Radiobutton is already selected?

The code:

import tkinter as tk

def on_choice():
    print('Function executed')

root = tk.Tk()
root.geometry('300x150')

radiobutton_variable = tk.StringVar()
radiobutton_variable.set(1)
button_1 = tk.Radiobutton(root, text='Button 1', variable=radiobutton_variable, value=1, command=on_choice)
button_2 = tk.Radiobutton(root, text='Button 2', variable=radiobutton_variable, value=2, command=on_choice)

button_1.pack()
button_2.pack()

root.mainloop()

Solution

A simple solution is to use a variable to track which Radiobutton was pressed last (I've called it prev_btn here).

The command function can inspect this value and only execute if it's changed from the last time the function was called. After that, the function stores the updated button value.

import tkinter as tk


def on_choice():
    # set prev_btn  as a global so this function can modify its value
    global prev_btn
    # only trigger the useful stuff if the button is different from last time
    if radiobutton_variable.get() != prev_btn:  # if button changed...
        print('Function executed')
        # store the value of the most recently pressed button
        prev_btn = radiobutton_variable.get()


root = tk.Tk()
root.geometry('300x150')

radiobutton_variable = tk.StringVar()
radiobutton_variable.set(1)

# define a variable to store the current button state
# (you could also set this to '1', but doing it this way means you won't have to
#  update the default value in two places in case you decide to change it above!)
prev_btn = radiobutton_variable.get()

button_1 = tk.Radiobutton(root, text='Button 1', variable=radiobutton_variable, value=1, command=on_choice)
button_2 = tk.Radiobutton(root, text='Button 2', variable=radiobutton_variable, value=2, command=on_choice)

button_1.pack()
button_2.pack()

root.mainloop()