Python, assigning values right way in lambda function

Question

I am trying to make a buttons that prints values what i assing to them. In my mind all buttons should print same values on their text value. Instead they all print "4". What is the wright way to solve this?

from tkinter import *

root = Tk()

def printFunc(text):
    print(text)

list=[0,1,2,3,4]

for i in list:

    w = Button(root, text=list[i],command=lambda: printFunc(list[i])).pack()

root.mainloop()

score 1 · Accepted Answer · answered Mar 05 '17 at 20:53

1

The solution is to provide a default value at the moment then lambda is constructed

from Tkinter import *


root = Tk()

def printFunc(text):
    print(text)

lst=[0,1,2,3,4]

for i in lst:

    w = Button(root, text=lst[i],command=lambda x=lst[i]: printFunc(x)).pack()

root.mainloop()

answered Mar 05 '17 at 20:53

rth

2,693
1
20
27

wow, thank you so much for your help :D <3 – yasinfy Mar 05 '17 at 20:56

score 1 · Answer 2 · answered Mar 05 '17 at 20:57

This is a very common beginners problem, because you don't understand how lambda works. The solution is to use functools.partial instead of lambda.

from tkinter import *
from functools import partial

root = Tk()

def printFunc(text):
    print(text)

list=[0,1,2,3,4]

for i in list:
    w = Button(root, text=list[i],command=partial(printFunc, list[i]))
    w.pack()

root.mainloop()

Also, always put the pack() on a new line, so that you avoid another very common beginners problem.

thank you for the reply! i understand what you mean, i will be careful next time :) — yasinfy, Mar 05 '17 at 21:12

Python, assigning values right way in lambda function

2 Answers2