Python Tkinter: Bind function to list of variables in a for-loop

Question

I’m building an application with a lot of buttons, so I use a list of them and a for-loop to bind a function to each of them that prints the button’s text when clicked. When I bind it to each button individually everything works fine, but when I use the for-loop every button only prints the text of the last item in the button list (which is "3" in this case).

import tkinter as Tk
from tkinter import *

win = Tk()

b1 = Button(win, text="1")
b1.grid(row=0)
b2 = Button(win, text="2")
b2.grid(row=0,column=1)
b3 = Button(win, text="3")
b3.grid(row=0,column=2)

button_list = [b1,b2,b3]

def printText(item):
    print(item["text"])

for button in button_list:
    button.bind("<Button-1>",lambda a:printText(button))

root.mainloop()

From what I’ve seen in similar questions this has something to do with lambda, however I’m not familiar with the lambda function and I’m struggling to understand how to go about fixing this.

Asked By: Natalie

||

Source

Answer 1

The reason of the behaviour is that all the lambdas use the same button variable, which contains the last button for the moment of pressing any button. The functions behaviour is called closure. You can pass every button in the loop by means of an argument with a default value. The approach lets us save each button in that argument, so each lambda would use its own button.

import tkinter as tk


def print_btn_text(item):
    print(item["text"])

root_win = tk.Tk()
b1 = tk.Button(root_win, text="1")
b1.grid(row=0)
b2 = tk.Button(root_win, text="2")
b2.grid(row=0, column=1)
b3 = tk.Button(root_win, text="3")
b3.grid(row=0, column=2)

button_list = [b1, b2, b3]
for button in button_list:
    button.bind("<Button-1>", lambda event, btn=button: print_btn_text(btn))

root_win.mainloop()

Answered By: I_Can_Help

Python Tkinter: Bind function to list of variables in a for-loop

Question:

Answers: