Return value using button

Question

I'm trying to return a value using a button, but i just can't get it to work. What i want is the button to return a value which later on can be used to check is the function was used or not. The code that I'm using is the following:

from Tkinter import *
master = Tk()
master.geometry("200x100")
def bla():
    return 1
Button(master, command = bla, text = 'OK').pack()

if bla == 1:
    print('1')

mainloop()

I've also tried to do this using lambda but i could not figure that one out too.

Solution 1

Try taking a look at this link https://stackoverflow.com/a/11907627/3110529 as it addresses the issues you're having.

The main concern is that callbacks are designed to just be a behaviour that happens in response to an event and therefore it doesn't entirely make sense for them to return a value. In your program, when you say

if bla == 1: print('1')

you're asking if the function pointer (or reference?) is equal to 1 which it obviously will never be.

You might be tempted to use global variables to cover this (i.e. store a 'blah' variable, then have the call back set its value) but this is generally considered bad practice. Instead, as in the link, try converting it to a class which will allow you to use member variables to store the results and responses of callbacks in a more organised manner.

Solution 2

Your problem is that you arn't saving the return value of bla().

You can do this using a global variable:

from Tkinter import *
master = Tk()
master.geometry("200x100")

gloBla = 0
def bla():
    global gloBla
    gloBla = 1
Button(master, command = bla, text = 'OK').pack()


mainloop()

if gloBla == 1:
    print('1')

Comments

[Readme]

This is actually better than the answer i wrote. Here, have my upvote.