How to create a tkinter toggle button?

You can import tkinter library (Use capital letter for python 2.7):

import Tkinter 

Create tkinter objects...

root = tk.Tk()

...and tkinter button

toggle_btn = tk.Button(text="Toggle", width=12, relief="raised")
toggle_btn.pack(pady=5)
root.mainloop()

Now create a new command button called "toggle" in order to create the effect of "toggle" when you press playing on the relief property (sunken or raised) :

def toggle():

    if toggle_btn.config('relief')[-1] == 'sunken':
        toggle_btn.config(relief="raised")
    else:
        toggle_btn.config(relief="sunken")

At the end apply this behaviour on your button:

toggle_btn = tk.Button(text="Toggle", width=12, relief="raised", command=toggle)

The background and fg are set only in the if-clause. You need to set them also in the else clause:

def onNightMode(self):
    if index:
        self.text.config(font=('courier', 12, 'normal'), background='black', fg='green')

    else:
        self.text.config(font=('courier', 12, 'normal'))

    index = not index

---

i.e.,

else:
    self.text.config(font=('courier', 12, 'normal'), background='green', fg='black')