Binding selected values of Combobox to subprogram

Question

My code:

import tkinter as tk
from tkinter import ttk

win = tk.Tk()

def assign():
    value = number.get()
    
    if value == 'op1':
        label = tk.Label(win, text = number)
        label.grid(column = 1, row = 0)

number = tk.StringVar()
box = ttk.Combobox(win, textvariable = number, state = 'readonly')
box['values'] = ('op1','op2','op3')

box.set('op2')

box.grid(column = 0, row = 0)

box.bind('<<ComboboxSelected>>', assign())


win.mainloop()

Explanation: this is how I think my program works.

box , which is the Combobox , has assigned a textvariable named number that, I suppose , takes the values of box , that is, ('op1', 'op2', 'op3') . box is then binded to a subprogram called assign() which will retrieve the value of number and set it equal to value . If value is equal to 'op1' , the subprogram will create and grid a label called label that will display the text 'Hello' . Unfortunately, this doesn't work. In other words, my objective is to, when the user selects one of the values given in box['values'] , assign() runs and, If the codition is met, display label .

Output:

As you can see, even though I selected 'op1' , label isn't displayed next to box .

Answer 1

You will have to remove the () while using bind to avoid function call, then create a label outside functions and then update it from the inside using config , like:

label = tk.Label(win)
def assign(event):
    value = number.get() # Get the value
    
    if value == 'op1':
        label.config(text=number) # Update the text
        label.grid(column = 1, row = 0)

box.bind('<<ComboboxSelected>>', assign) # Remove the ()

This way you don't rewrite the labels and just update the labels with new values.

But I think there is no use of StringVar here, just remove it and use box.get() to get the value from the combobox. So according to me the best practice would be:

import tkinter as tk
from tkinter import ttk

win = tk.Tk()

label = tk.Label(win) # Create this outside of function

def assign(event):
    value = box.get() # Get value from combobox
    
    if value == vals[0]: # Check the selected item with the values tuple
        label.config(text=value) # Update the text of label
        label.grid(column=1,row=0)

vals = ('op1','op2','op3') # Tuple of values
box = ttk.Combobox(win,values=vals,state='readonly') # Add value option
box.current(1) # Set the second item as current value
box.grid(column=0,row=0)

box.bind('<<ComboboxSelected>>', assign)

win.mainloop()

Answer 2

import tkinter as tk
from tkinter import ttk

win = tk.Tk()

label = tk.Label(win)  # Create this outside of function


def assign(event):
    value = box.get()  # Get value from combobox

    if value == vals[0]:  # Check the selected item with the values tuple
        label.config(text=value)  # Update the text of label
        label.grid(column=1, row=0)
    elif value == vals[1]:  # Check the selected item with the values tuple
        label.config(text=value)  # Update the text of label
        label.grid(column=1, row=0)
    elif value == vals[2]:  # Check the selected item with the values tuple
        label.config(text=value)  # Update the text of label
        label.grid(column=1, row=0)


vals = ('op1', 'op2', 'op3')  # Tuple of values
box = ttk.Combobox(win, values=vals, state='readonly')  # Add value option
box.current(1)  # Set the second item as current value
box.grid(column=0, row=0)

box.bind('<<ComboboxSelected>>', assign)

win.mainloop()