Member Avatar for Friendly Lotus

Hi all,
I am trying to update the colour of a Tkinter label, so as the value of a variable changes so to does the colour of the text.
Below is a simple example of what I am trying to achieve, but the problem is when I press the button I want the labels colour to update to red.

from Tkinter  import *
root = Tk()
colour = StringVar()
colour.set('blue')
def colourUpdate():
    colour.set('red')
    root.update()
    
btn = Button(root, text = "Click Me", command = colourUpdate)
l = Label(root, textvariable=colour, fg = colour.get())
l.pack()

btn.pack()
root.mainloop()
  • 3 Contributors
  • 2 Replies
  • 15K Views
  • 7 Hours Discussion Span
  • Latest Post Latest Post by TrustyTony

Dani AI

Generated

textvariable only updates the label’s text; it does not bind other options like fg. Instead of calling root.update() (which is rarely needed and can cause re-entrancy issues), tie the StringVar to the label’s color with a variable trace so the UI updates automatically when the variable changes.

from Tkinter import Tk, StringVar, Label, Button

root = Tk()
color = StringVar(value='blue')

lbl = Label(root, textvariable=color)
lbl.pack()

def on_color_change(*_):
    lbl.configure(fg=color.get())  # keep color in sync with the variable

color.trace('w', on_color_change)  # Python 2
Button(root, text='Set red', command=lambda: color.set('red')).pack()

root.mainloop()

Notes:

  • In Python 3, import tkinter, and use trace_add('write', callback) instead of trace. See tkinter variables and traces.
  • For periodic or delayed updates, prefer widget.after(ms, func) over update(); see after.
  • If you switch to ttk.Label, the foreground is controlled by a style (e.g., Style().configure('My.TLabel', foreground='red')) rather than fg. The classic Label options are documented in the Tk man page: label options.

Recommended Answers

All 2 Replies

Member Avatar for slate

The label's fg option is not executed when root.update is called. It does not seem logical.
You should set the fg option of the label in the command somehow. I am not an expert int tkinter, but recreating it is always a possibility.
Textvariable applies only for the text option. As far as I read the docs.

def colourUpdate():
    l.config(fg='red')
    root.update()
Edited by slate because: n/a
Member Avatar for TrustyTony

Like this?

from Tkinter  import *
def colourUpdate():
    colour.set('red' if colour.get()!='red' else 'blue')
    print colour.get()
    l.configure(fg=colour.get())

root = Tk()
colour = StringVar()
colour.set('red')
    
btn = Button(root, text = "Click Me", command = colourUpdate)
l = Label(root, textvariable=colour, fg = colour.get())
l.pack()

btn.pack()
root.mainloop()

l is not the most recommendable variable name.

Edited by TrustyTony because: n/a
Be a part of the DaniWeb community

We're a friendly, industry-focused community of developers, IT pros, digital marketers, and technology enthusiasts meeting, networking, learning, and sharing knowledge.