Tkinter: how to change label text

Changing the text on a tk.Label should be easy, right?

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Start with importing the tkinter library for python 3 and creating the tk app. The tk.Tk() object is responsible for going out and speaking to the operating system on your computer and requesting a window with min/max/close buttons, the ability to grab/resize etc. The root is the name traditionally given to the base object that sits inside this window, and you can only have one base object:

import tkinter as tk
root = tk.Tk()

Now create the label, give it a parent (in this case root) and add some text:

my_label  = tk.Label(root, text="hello, learn-data.org")

… and then pack (easiest of the three layout managers):

my_label.pack()

That’s it for generating the text for a label. To see it in action, fire off the root mainloop:

root.mainloop()

The full code looks like this:

import tkinter as tk
root = tk.Tk() 
my_label  = tk.Label(root, text = "hello, learn-data")
my_label.pack()
root.mainloop()

And you should get this:

tk.Label: Let’s change the text

If you run this bit of code below where you’ve declared the my_label object:

print(help(my_label))

you’ll see that my_label is in fact a Label object (duh), with the following options:

and text is in there. In fact all standard options can be called up (with the appropriate parameters) along the following lines:

my_label['text'] = "goodbye, cruel world"

We want to test this and see if it will change the text of the label. It would be nice if we could press a button to see the before and after effects. Modify your code as follows:

import tkinter as tk
root = tk.Tk() 
my_label  = tk.Label(root, text = "hello, learn-data")
my_label.pack()
my_btn = tk.Button(root, text = "press to change", command = change_text)
my_btn.pack()
root.mainloop()

Depending on what editor you’re using you should see change_text is highlighted. This is because the code will look for a function with that name – and there isn’t one. Add this change_text() function anywhere above the my_btn line ( I usually keep my functions near the top of the code):

import tkinter as tk
def change_text():
    my_label['text'] = "goodbye, cruel world"
root = tk.Tk() 
my_label  = tk.Label(root, text = "hello, learn-data")
my_label.pack()
my_btn = tk.Button(root, text = "press to change", command = change_text)
my_btn.pack()
root.mainloop()

The second way to change label text is to use config (short for configure):

def change_text():
    my_label.config(text = "goodbye, cruel world")

This works just like before.

The third way is to pull out the text as a string variable. It’s a little more complicated, but gives you more options down the road. Notice you have to change text to textvariable:

my_text = tk.StringVar()
my_text.set('hello, learn-data')
my_label  = tk.Label(root, textvariable = my_text)

And you would change it by using .set(‘text’) as follows:

def change_text():
    my_text.set('goodbye, cruel world')

Full code here:

import tkinter as tk
def change_text():
    my_text.set('goodbye, cruel world')
root = tk.Tk() 
my_text = tk.StringVar()
my_text.set('hello, learn-data')
my_label  = tk.Label(root, textvariable = my_text)
my_label.pack()
my_btn = tk.Button(root, text = "press to change", command = change_text)
my_btn.pack()
root.mainloop()

(Any use? claps are nice, or you can comment/ask questions…)