How to call an action when a button is clicked in Tkinter

Question

I am experimenting with Tkinter for the first time, and am trying to call a function when a button is clicked. This is part of my code. mt is referring to a label that I have made dynamic by attaching it to a label so that I can change what the label says. I want the user to be able to type in something into an entry box, hit the button, and the it will change the label to what was typed.

    def new(self):
        mt.set("New")
        e1 = Entry(master)
        e1.pack()
    def new_ok(self):
        mt.set("OK")
        #the next part is what I need help with
        if (checks if button has been clicked) button has been clicked:
            mt.set("#what it says in the entry box#")

How should I do this? I have looked on tutorials and read them but none of them have clearly acknowledged how to check if a button has been pressed and to respond.

It's almost as if you are trying to create your own event loop, which is Tkinter's job, not yours. Tkinter has a "don't call me, I'll call you" policy here. You give it a callback and it calls it when the right event fires. The link in John Gaines Jr's answer shows how it's done. — Steven Rumbalski, Apr 19 '12 at 22:20

score 2 · Answer 1 · answered Apr 19 '12 at 22:17

2

I'm no Tkinter wiz, but one of the first things I see in the module docs for Tkinter is A Simple Hello World Program, which has the answer to your question in it. (As with most GUI toolkits, the answer is callback or event handler functions.) The member function say_hi is a callback for the Hello button.

answered Apr 19 '12 at 22:17

John Gaines Jr.

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Thanks, but I also wanted to know how to call the entry in the new function when the entry is defined in a different function – udpatil Apr 20 '12 at 00:01

Honest Abe · Accepted Answer · 2012-04-20T07:00:46.937

If the question is: "How do you update a Label widget?"
then the answer is with the widget's configure method.

# Tkinter in Python 2.7 & tkinter in 3.2
import Tkinter as tk

class GUI(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)

        bF = tk.Frame(self, bd=8, relief='sunken')
        bF.pack(expand='true', fill='x')
        changeButton = tk.Button(bF, text='Change', bd=4, fg='white',
                                relief='groove', activebackground='green',
                                command=self.change_label)
        changeButton.pack()

        self.entryLabel = tk.Label(self, text='Hello')
        self.entryLabel.pack()

        self.mEntry = tk.Entry(self, bd=4, relief='sunken')
        self.mEntry.pack()

    def change_label(self):
        data = self.mEntry.get()
        self.entryLabel.configure(text=data)


gui = GUI()
gui.mainloop()

You will want to make your GUI a class like in this example;
that way you can use the self. prefix to refer to the widget made in another method.

In your example it looks like you might be saying 'mt' is a control variable.
The answer would still be to make a class, so that you can use the self. prefix.

The control variable likely isn't necessary unless you would want
the label to be updated as you changed the contents of the Entry widget:

import Tkinter as tk

class GUI(tk.Tk):
    def __init__(self):
        tk.Tk.__init__(self)

        bF = tk.Frame(self, bd=8, relief='sunken')
        bF.pack(expand='true', fill='x')

        var = tk.StringVar()
        var.set('Hello')
        entryLabel = tk.Label(self, textvariable=var)
        entryLabel.pack()

        mEntry = tk.Entry(self, bd=4, relief='sunken', textvariable=var)
        mEntry.pack()

gui = GUI()
gui.mainloop()

How to call an action when a button is clicked in Tkinter

2 Answers2

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