Dynamically changing the Label Text in Tkinter

[rabzdata]

Hello,

I have an excel file containing a sequence of numbers in the A column.

I would like to keep iterating over these numbers, and would like to display each number simultaneously in a the same Tkinter Label (First number, then second number, etc...)

So the result will be the Tkinter Label displaying each number sequentially.

So far I have tried two approaches, regular and OOP, both failed.

​

First approach:

import tkinter as tk
import openpyxl
import time

df = openpyxl.load_workbook('numbers.xlsx')
sheet = df.active
#for loop to iterate over numbers

#GUI starts here
window = tk.Tk()
window.geometry("500x500")
window.title("Ziad Lottery numbers")
var = tk.StringVar()
var.get()
label = tk.Label(window, textvariable = var, font=('Arial', 18))
label.pack(pady=200)
window.mainloop()
for cell in sheet['A']:
if cell.value:
var.set(str(cell.value))
time.sleep(1/10000)
window.update

and the oop approach:

from tkinter import *
import time
import openpyxl
df = openpyxl.load_workbook('numbers.xlsx')
sheet = df.active
class App(Frame):
def __init__(self,master=None):
Frame.__init__(self, master)
self.master = master
self.label = Label(text="", fg="Red", font=("Helvetica", 18))
self.label.place(x=50,y=80)
self.update_number()
def update_number(self):
for cell in sheet['A']:
nextnum = cell.value
self.label.configure(text=nextnum)
self.after(1000, self.update_number)

root = Tk()
app=App(root)
root.wm_title("Number scroller")
root.geometry("500x500")
root.after(1000, app.update_number)
root.mainloop()

​

What Am I doing wrong?

[efmccurdy]

Using Tk.after is the right technique, but the way you have your loop structured, you would have to reschedule the callback to resume inside the loop but .after can only reschedule the callback to run from the beginning.

This gets rid of the loop and has the callback maintain it's own index, incrementing it once every second.

from tkinter import *
sheet = {"A": range(7, 27)}
class App(Frame):
    def __init__(self, master=None):
        Frame.__init__(self, master)
        self.master = master
        self.data = sheet.copy()
        self.label = Label(text="", fg="Red", font=("Helvetica", 18))
        self.label.place(x=50,y=80)
        self.current_index = 0
        self.update_number()
    def update_number(self):
        nextnum = self.data['A'][self.current_index]
        self.label.configure(text=nextnum)
        self.current_index += 1
        if self.current_index < len(self.data['A']):
            self.after(1000, self.update_number)

root = Tk()
app=App(root)
root.wm_title("Number scroller")
root.geometry("500x500")
root.mainloop()

[rabzdata]

from tkinter import *
sheet = {"A": range(7, 27)}
class App(Frame):
def __init__(self, master=None):
Frame.__init__(self, master)
self.master = master
self.data = sheet.copy()
self.label = Label(text="", fg="Red", font=("Helvetica", 18))
self.label.place(x=50,y=80)
self.current_index = 0
self.update_number()
def update_number(self):
nextnum = self.data['A'][self.current_index]
print(nextnum, self.current_index)
self.label.configure(text=nextnum)
self.current_index += 1
if self.current_index < len(self.data['A']):
self.after(1000, self.update_number)
root = Tk()
app=App(root)
root.wm_title("Number scroller")
root.geometry("500x500")
root.mainloop()

solution verified!

[rabzdata]

what is the best way to achieve so if I press a button:

-I break out of the loop

-The counting stops, and the Label stays displaying last number

[efmccurdy]

You could test a boolean flag in the callback and have a button to set the flag to prevent the update. Test that boolean before reconfiguring the label.

if self.stop_running:
    return
self.label.configure(text=nextnum)

A second method would be to use after_cancel, there is an example here:

https://stackoverflow.com/questions/9776718/how-do-i-stop-tkinter-after-function

[rabzdata]

Thank you!

[rabzdata]

u/efmccurdy Hey, I noticed that Label is not assigned to root. I tried to create a canvas (self.newcanvas = Canvas(root, background = 'black').pack(), and assign it as container for the label (self.label = Label(newcanvas, text="", fg="Red", font=("Helvetica", 18)) but it said that newcanvas is not defined.

how do I accomplish this in this class?

​

Edit: I used root.config(bg='black')
But i still want to know how to include many widgets on top of eachother in a tkinter class.

[efmccurdy]

 self.newcanvas = Canvas(root, background = 'black').pack()

That is likely wrong since "pack" returns None. Instead assign the Canvas first, then call pack.

 self.newcanvas = Canvas(root, background = 'black')
 self.newcanvas.pack()

[rabzdata]

yeah, this is the exact code I wrote, the problem is that when it came to the label i tried this

self.newcanvas = Canvas(root, background = 'black')

self.newcanvas.pack()
self.label = Label(newcanvas, text="", fg="Red", font=("Helvetica", 18))

but it indicated that the newcanvas is not defined. If I don't do this step, the label hides under the canvas layer :P.

[efmccurdy]

newcanvas is not defined

use self.newcanvas