Disable / Enable Button in TKinter

The problem is in your switch function.

def switch():
    b1["state"] = DISABLED

When you click the button, switch is being called each time. For a toggle behaviour, you need to tell it to switch back to the NORMAL state.

def switch():
    if b1["state"] == NORMAL:
        b1["state"] = DISABLED
    else:
        b1["state"] = NORMAL

A Tkinter Button has three states : active, normal, disabled.

You set the state option to disabled to gray out the button and make it unresponsive. It has the value active when the mouse is over it and the default is normal.

Using this you can check for the state of the button and take the required action. Here is the working code.

from tkinter import *

fenster = Tk()
fenster.title("Window")

def switch():
    if b1["state"] == "normal":
        b1["state"] = "disabled"
        b2["text"] = "enable"
    else:
        b1["state"] = "normal"
        b2["text"] = "disable"

#--Buttons
b1 = Button(fenster, text="Button", height=5, width=7)
b1.grid(row=0, column=0)    

b2 = Button(text="disable", command=switch)
b2.grid(row=0, column=1)

fenster.mainloop()