[Python] How to change a buttons state from disabled to active when an option is selected in...

I'm trying to change the button state when an option is selected in the option menu, but nothing is changing. Can anyone tell me what I'm doing wrong?

from tkinter import *

def setLabel():
changed.set("Active")

def changeState():
pick = choose.get()
if (pick == "op2"):
button['state'] = button.ACTIVE
button.config(text = "ACTIVE")
else:
button['state'] = app.DISABLED
button.config(text = "Disabled")

app = Tk()
app.resizable(40,40)

choose = StringVar()
choose.set("op1")
options = OptionMenu(app, choose, "op1", "op2")
options.pack()


button = Button(app, text = "Disabled", state = DISABLED, command = setLabel)
button.pack()

changed = StringVar()
label = Label(app, textvariable = changed, font = ("helvetica", 10))
label.pack()

app.mainloop()

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