Using class structure with Python protocol delete window handlers

Question

I have the following program using Tkinter in Python. it works well in its simple format but gives me errors when I try converting it to a class approach. I'm tracking a previous Tkinter GUI session by storing entered values in a text file and creating a handler to track the end of the session. WHen a new session is opened, the entry value from the previous session is already displayed in the entry box

#!usr/bin/env python
from Tkinter import *

# Define input retrieve function for application input
def retrieve_text():
    print(app_entry.get())

def handler():
    f = open("backup.txt", "w")
    f.write(app_entry.get())
    f.close()
    app_win.destroy()

if __name__ == "__main__":

    # Create window (or form)
    app_win = Tk()

    # Create label
    app_label = Label(app_win, text="Enter value")
    app_label.pack()

    # Create entry box
    t = open("backup.txt")
    var1 = t.readlines()
    Text = StringVar()
    Text.set(var1[0])
    app_entry = Entry(app_win,textvariable=Text)
    app_entry.pack()

    # Create button
    app_button = Button(app_win, text="Print Value", command=app_win.retrieve_text)
    app_button.pack()

    app_win.protocol("WM_DELETE_WINDOW", handler)
    # Initialize GUI loop
    app_win.mainloop()

When I try to convert to a class based approach, I get an error "MyGUI instance has no attribute named protocol". My class structure is as follows:

#!usr/bin/env python
from Tkinter import *

class Tracker(Frame):
    def __init__(self):
        Frame.__init__(self)

        # Create label
        app_label = Label(self, text="Enter value")
        app_label.pack()

        # Create entry box
        t = open("backup.txt")
        var1 = t.readlines()
        Text = StringVar()
        Text.set(var1[0])
        app_entry = Entry(self,textvariable=Text)
        app_entry.pack()
        # Create button
        app_button = Button(self, text="Print Value", command=self.retrieve_text)
        app_button.pack()

        self.entry1 = app_entry.get()

        self.protocol("WM_DELETE_WINDOW", self.handler)

    def retrieve_text():
        print(self.entry1)

    def handler():
        f = open("backup.txt", "w")
        f.write(self.entry1)
        f.close()
        self.destroy()

if __name__ == "__main__":

    # Create window (or form)
    app = Tracker()
    # Initialize GUI loop
    app.mainloop()

Could anyone tell me what I'm doing wrong? Is the location where I'm specifying my "WM_DELETE_WINDOW" correct?

noob oddy · Accepted Answer · 2012-02-22 23:14:29Z

2

Your Tracker class is a Frame.

self.protocol("WM_DELETE_WINDOW", self.handler) # is meant to be used with a Toplevel or root window.

edited Feb 22, 2012 at 23:14

answered Feb 22, 2012 at 22:46

noob oddy

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Comments

Bryan Oakley · Accepted Answer · 2012-02-21 12:03:33Z

1

I think it's going to be hard for us to tell you what is wrong with your class-based approach when you show us the original, working code instead of the non-working class-based code.

That being said, I can answer the question "Where exactly do I initialize the 'WM_DELETE_WINDOW' command?". You initialize it in the constructor of your application object.

class MyApp(Tk):
    def __init__(self, *args, **kwargs):
        Tk.__init__(self, *args, **kwargs)
        ...
        self.protocol("WM_DELETE_WINDOW", self.handler)

answered Feb 21, 2012 at 12:03

Bryan Oakley

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1 Comment

prrao Over a year ago

Sorry about that. My updated question shows what I've been trying.

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