tkinter_adding_button.py

from tkinter import *

class Window(Frame):

    def __init__(self, master = None):
        Frame.__init__(self, master)

        self.master = master

        self.init_window()

    def init_window(self):

        self.master.title("GUI")

        self.pack(fill=BOTH, expand=1)

        quitButton = Button(self, text="Quit", command=self.client_exit)

        quitButton.place(x=0, y=0)

    def client_exit(self):
        exit()
        
root = Tk()
root.geometry("400x300")

app = Window(root)

root.mainloop()