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I am new to coding and trying to figure this out and I cannot, and I can't seem to find any videos on youtube that shows this either.

Essentially what i want to do is have a loop running, and be able to click a button and it change a variable in the loop. For instance:

from tkinter import *
import time

root = Tk()
x = 0

def changeVariable():
    x = x + 5

button1 = Button(root, text="add 5", command=changeVariable)
button1.pack()

while True:
    root.mainloop()
    while x > 0:
        print("X is greater than 0")
        x = x - 1
        time.sleep(1)
    else:
        print("Please click the button")
        time.sleep(1)

I have tried all sorts of things and i cannot get the button to change the value of X in my while loop. Can someone please explain how to do this or link a video/guide that does a good job explaining this to a novice?

Thanks

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2
  • You definitely don't want to call mainloop in a loop. It should be called exactly once. Commented May 28, 2019 at 19:59
  • When/where do i call it? I cannot seem to get the window to appear WHILE the while loop is running. I can either get the window to appear (Which will give me x is undefined error when pressed) or the while loop which just always says to press the button. I'm trying to figure out how to get them to run together.... Commented May 28, 2019 at 20:00

1 Answer 1

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You cannot put code after the mainloop. You do not need root.mainloop as there is a forever loop already in your code. You can just remove root.mainloop and your code should work.

Edit: Another issue is that x is not defined globally. At the beginning of the changeVariable function, add the code global x.

The final issue is that you use time.sleep(). You don't want to use a time.sleep as the button could be pressed while everything is frozen. See edit 2 for a fix.

Edit 2:

You can use the tkinter after method. The after method can be applied to any tkinter object. In this case, we will apply it to root. This is the basic syntax: root.after(milliseconds, function_to_execute_after_wait). The function to execute is optional. In your case, instead of time.sleep(1), you should use root.after(1000). Make sure to add a root.update() after your root.after(1000).

You can also use += or -= for changing variables. Instead of x = x + 5, you can use x += 5. Instead of x = x - 1, you can use x -= 1.

Final Code:

from tkinter import *

root = Tk()
x = 0

def changeVariable():
    global x
    x += 5

button1 = Button(root, text="add 5", command=changeVariable)
button1.pack()

while True:
    while x > 0:
        print("X is greater than 0")
        x -= 1
        root.after(1000)
        root.update()
    else:
        print("Please click the button")
        root.after(1000)
        root.update()
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5 Comments

When i remove root.mainloop() the tkinter box with the button does not appear. When i have root.mainloop appear and i click it, it tells me that x is not defined and it cannot change it.
Also, my while loop does not start printing any messages until i exit it. I want them to run together, not independently....
@Lzypenguin Everything should be fixed now, please see my edits.
After your updates this worked!! Thank you so much! So now i am having issues with this working in my actual script. I have to repeatedly click the button over and over until it clicks right at the exact right time. I think this is because i'm using time.sleep(). What would you recommend that would be better than time.sleep()?
@Lzypenguin I have written the final code in my answer so you can see what it should look like in the end.

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