[Python] Why am I getting "UnboundLocalError local variable 'coffee_machine' referenced before...

coffee_machine = True

def user_input():
while coffee_machine:
user_choice = input("What type of coffee would you like espresso/latte/cappuccino?")
if user_choice == "off".lower():
coffee_machine = False
x = []
for ingredients in MENU[user_choice].get("ingredients").values():
x.append(ingredients)
print(x)

user_input()

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